Game On Euro-Atlantic

“Inasmuch as arms control efforts seek to affect future events, we have to be conscious of the degree of our uncertainty about the future, in which we are instructed by our experience with surprise in the past. Perhaps an appreciation for this uncertainty will inhibit our choice of arms control objectives, but if so, that is simply the way the ball bounces.”

– Bernard Brodie

The end of the war in Ukraine could present unique opportunities for arms control and reducing the risk of further instability in the Euro-Atlantic region. With the New Strategic Arms Reduction Treaty (New START) set to expire in February 2026, arms control as we know it is at risk of ending, with no clear successor to facilitate further cooperative efforts to reduce or limit strategic forces. Despite pressure for a peace settlement in Ukraine and follow-on arms control measures, Europe appears likely to remain a theater of instability due to increasing reliance on nuclear weapons, Russian territorial ambitions, and a weakening nuclear order. Additionally, the United States’ gradual shift away from Europe and toward the Indo-Pacific over the past decade has created the potential for a deterrence gap in the region. With these challenges in mind, what might arms control look like after the war in Ukraine?

The CSIS Project on Nuclear Issues set out to explore prospects for arms control with Russia following the end of the war in Ukraine. The project developed four alternative futures and two black swan scenarios for the Euro-Atlantic security environment after the war in Ukraine ends and convened a series of scenario-based discussions with cross-generational U.S. and European experts. The alternative futures approach allowed the authors to avoid the perennial challenge of tracking a moving target and instead identify consistent trends, along with potential moments of opportunity, for strengthening strategic stability and arms control. The scenarios included bloc competition, strategic disadvantage, strategic advantage, disordered competition, a change of leadership in Moscow, and nuclear use.

The scenario-based discussions and analysis yielded two main findings: Competition with Russia is unlikely to end, and Europe is poised to emerge as an increasingly influential player in strategic stability and arms control in the Euro-Atlantic region. The project also identified findings from the black swan scenarios, including that arms control is personality agnostic and that a change of leadership in the Kremlin will not necessarily lead to a breakthrough in arms control in the short term. Additionally, the nuclear order—including the nuclear taboo—is weakening and requires immediate attention as part of any future arms control agenda. The implications of these findings are that future arms control efforts will have to work in tandem with geostrategic competition, and enhancing deterrence should be the top priority. As such, arms control mechanisms will need to be flexible, and creating time limits on agreements is one particular tool for facilitating cooperation in an era of strategic competition.

Based on the project’s findings, the authors identified six opportunities for arms control after the war in Ukraine, which include specific recommendations for the United States, key actors within Europe, the P5 (the five recognized nuclear weapon states under the Nuclear Non-Proliferation Treaty [NPT]—China, France, Russia, the United Kingdom, and the United States), and nonnuclear weapon states committed to strengthening norms of non-use.

1. The Trump administration should immediately pursue talks with Russia to agree to observe New START central limits for up to three years after the treaty expires in February 2026. This agreement should rely on national technical means for verification while establishing a standing arms control dialogue to provide transparency into its implementation and explore opportunities for a more permanent, long-term agreement.

2. The United States should enhance its nuclear deterrent by preparing to upload warheads if Russia violates the three-year agreement, expanding capacity in the National Labs, and developing additional delivery platforms, including nuclear sea-launched cruise missiles and a new stand-off capability. All of these measures can be paused or rolled back in the event of a breakthrough in arms control.

3. Europe should develop a new strategy for deterrence and arms control that prioritizes flexibility. Specific steps for strengthening deterrence should include increased defense spending and a coordinated effort to increase defense production, such as by adopting a “comparative advantage” approach, in order to take on a greater burden-sharing role within NATO and to hedge against an uncertain future. Additionally, France and the United Kingdom should modestly expand their strategic arsenals—such as by reintroducing an air leg of the British deterrent—and France should join the NATO Nuclear Planning Group as an observer.

4. Europe should remain open to nuclear arms control opportunities, such as time-bound cooperative efforts, and continue to promote the Vienna Document as a tool for conventional arms control and transparency building. Such efforts will not only create opportunities for engaging with Russia—and potentially China—but also demonstrate an enduring commitment to arms control and the NPT.

5. The NPT P5 process should establish a Crisis Stability Initiative to identify risks of nuclear escalation during the war in Ukraine through a series of dialogues aimed at sharing national perceptions throughout the conflict. The initiative should also develop a crisis stability tool kit, and the P5 should agree to a set of shared commitments regarding crisis communication and risk reduction.

6. States from the Global South, or Global Middle Ground, should issue a joint statement in NPT and UN forums calling on all parties to continue to abide by the Comprehensive Test Ban Treaty and the Outer Space Treaty. States Parties to the Treaty on the Prohibition of Nuclear Weapons should issue a joint statement in NPT forums condemning the role of nuclear threats in Russia’s war in Ukraine and stop treating all nuclear-armed states as a monolith. Instead, they should seize this unique and powerful opportunity for strengthening strategic stability by upholding norms of non-use.

This more flexible approach to arms control in an era of strategic competition admittedly comes with challenges. Any nuclear or conventional buildup could be perceived as escalatory by Moscow and Beijing. Europeans may struggle to develop a united, consistent, and coordinated strategy for deterrence and arms control. Additionally, a more competitive approach by the United States and Europe could become a self-fulfilling prophecy, undermining both prospects for arms control with Moscow and assurance among allies. It is essential, therefore, that Washington and European capitals consistently demonstrate an openness to arms control and dialogue, and put the ball in Moscow and Beijing’s court to meaningfully engage in strengthening strategic stability and ushering in a new era of arms control.

Introduction

It is winter 2027. Europe has enjoyed two years of relative calm following a peace settlement between Russia and Ukraine in which Moscow secured territorial gains and imposed limits on Ukraine’s military forces. Ukrainian President Volodymyr Zelensky has been forced out of power in Kyiv. Immediately following the peace settlement, U.S. President Donald J. Trump and Russian President Vladimir Putin secured an arms control agreement to maintain the central limits of the 2010 New Strategic Arms Reduction Treaty (New START) for an additional five years after its expiration in 2026. The Trump administration is moving ahead with plans to withdraw the U.S. conventional military presence from Europe, and the credibility of U.S. nuclear guarantees to Europe is questionable. European governments are struggling to maintain public support for defense spending following the 2025 peace settlement. Intelligence now shows that not only has Russia ignored the agreed-upon limits on its strategic delivery systems, but it is also just weeks away from deploying a nuclear weapon in space, in violation of the Outer Space Treaty (OST). Additionally, Russia has begun amassing troops on its border with Moldova, in the contested region of Transnistria. What options does NATO have to respond?

This hypothetical scenario demonstrates the risk of chronic instability in Europe following the war in Ukraine. Russia’s regional ambitions and nuclear rhetoric, dating back at least to its 2008 invasion of Georgia, suggest that Moscow may not want stability in Europe. Instead, it is pursing instability and increasing nuclear risks to achieve its strategic objectives. The scenario also tests the limits of what is possible for arms control. In recent years, the United States has repeatedly approached Russia to re-engage in strategic stability dialogues, but Moscow has consistently refused. As a justification for suspending participation in New START in 2023, for example, Putin pointed to fundamental disagreements about Euro-Atlantic security and claimed, “They (NATO) want to inflict a strategic defeat on us and also to get to our nuclear sites.” When New START expires in February 2026, a rich historical legacy of strategic arms control could die with it, and there may be no returning to the status quo ante for arms control.

The CSIS Project on Nuclear Issues set out to explore prospects for arms control with Russia following an end to the war in Ukraine. The project developed four alternative futures and two black swan scenarios for the Euro-Atlantic security environment after the war ended and convened a series of scenario-based discussions with cross-generational U.S. and European experts. The alternative futures approach allowed the authors to avoid the perennial challenge of tracking a moving target and instead identify consistent trends, along with potential moments of opportunity, for strengthening strategic stability and arms control.

Across all six scenarios, which included variations in Russian military prowess and alliance unity, experts agreed that the United States and its allies should not assume that Russia’s territorial ambitions will be satisfied by a peace settlement with Ukraine. Instead, Moscow may actually be emboldened by the outcome of the war in Ukraine—whether favorable or unfavorable—and continue to increase reliance on nuclear threats. Another important finding was that a united Europe has the potential to become a major player in strategic stability and arms control. In her speech at the 2025 Munich Security Conference, European Union President Ursula von der Leyen said there was a “need for Europe not only to speak frankly but also to act accordingly. I believe that when it comes to European security, Europe has to do more.” Because of the interrelationship between deterrence and arms control, “doing more” may not only entail enhancing conventional deterrence but also playing a more influential role in prospects for strategic arms control.

What this means for the United States and Europe is that any arms control agreements will need to prioritize and work in tandem with enhancing deterrence, while allowing for flexibility in responding to an uncertain and dangerous geopolitical landscape. Historically, strategic stability has been defined in terms of the United States’ and Russia’s perception that they possess survivable second-strike nuclear forces. In 2023, the bipartisan Congressional Commission on the Strategic Posture of the United States, or the Strategic Posture Commission, defined strategic stability as “A condition in which the political relations and military balance between states that pose an existential threat to each other is such that they perceive neither a compelling need nor a viable opportunity to use military force to advance their interests at the expense of the other state.” This definition allows for a broader approach to strategic stability, including nonnuclear capabilities, along with the underlying political incentives driving competition. However, to be sure, strategic stability remains a contested term. Arms control, as a tool for strengthening strategic stability, need not happen in the absence of competition, but rather can occur in a worsening security environment, between potential adversaries, without necessarily involving like-for-like exchanges. It might not even focus on capabilities but could instead facilitate communication in the midst of an ongoing rivalry. Another implication of the project’s findings is that while historically strategic stability has been a two-player game, increasing European strategic autonomy, along with the rise of China, requires rethinking what strategic stability looks like in a multiplayer game and how to strengthen it.

This report proceeds in three sections. First, it provides a brief summary and analysis of the six alternative futures and their implications for arms control. Second, it presents the project’s main findings. The primary findings from across the scenarios include enduring competition and a growing role for Europe, but other findings touch on the potential for arms control in the event of leadership changes and the health of international institutions and norms. Finally, the report provides an arms control agenda for the United States and Russia, Europe, the P5, and the wider international nuclear order. It identifies time-bound agreements as a likely tool for pursuing arms control in an era of strategic competition, while allowing for flexibility. The third section also identifies key questions for “player Europe” to address in considering its new role in the international system. It outlines various policy options for how Europe might pursue deterrence and arms control in tandem, ranging from extreme autonomy to bilateral alliances. The end of the war in Ukraine will not be the end of Russia’s destabilizing ambitions. The game is now on for Europe to rearm, coordinate a strategy for deterrence and assurance in the Euro-Atlantic, and embrace a more influential role in arms control.

Arms Control Futures

Arms control and deterrence have worked in tandem at least since the 1967 Harmel Report, which recognized NATO’s “first function” as deterrence while also recommending a “balanced reduction of military forces” and concluding that “Military security and a policy of détente are not contradictory but complementary.” Stimson Center Co-Founder Michael Krepon’s definition of arms control, which includes a range of mechanisms—from legally binding treaties to informal agreements on crisis communication—directly ties it to deterrence: “Deterrence requires effective lines of communication, codes of conduct, tacit understandings, political compacts, and formal treaties to help prevent the battlefield use of nuclear weapons. We call these diplomatic methods of reassurance arms control. The fundamental purposes of arms control are to stabilize nuclear rivalries and reduce nuclear danger.” The end of the war in Ukraine may prove to be a unique opportunity for these arms control mechanisms, either as part of a peace settlement or in the aftermath of any political rapprochement. Given the rapidly changing state of play in European security, along with the tattered state of arms control, exploring opportunities for arms control presents a methodological challenge.

This project used an alternative futures methodology to develop scenarios for the Euro-Atlantic security environment in late 2027. The scenarios accounted for variations in adversary capabilities, along with cooperation between Russia, China, Iran, and North Korea, and for differences in NATO alliance cohesion—ranging from renewed NATO unity to the waning credibility of U.S. extended nuclear deterrence in Europe. The scenarios also incorporated a range of potential outcomes from the war in Ukraine, such as a peace settlement favorable to Russia and European security guarantees to Ukraine. The scenarios are captured in Table 1, with full descriptions provided in Appendix A, and are characterized from the perspective of the NATO alliance.

▲ Table 1: Scenarios for Euro-Atlantic Security

The project also included black swan scenarios involving a change of leadership in Moscow and the use of nuclear weapons to account for significant developments that could shape the future of arms control but were not covered in the alternative futures. The scenarios were then discussed in a series of expert workshops with U.S. and European participants. Additionally, CSIS held a workshop with early-career researchers, which proved valuable in identifying a potentially important generational difference in attitudes toward institutions, as discussed below. For each scenario, participants identified (1) Russian, U.S., and European strategic objectives; (2) potential points of leverage to incentivize Russian participation in arms control; and (3) specific arms control opportunities. While the discussions largely focused on opportunities for nuclear arms control, conventional and non-kinetic capabilities were also considered in the scenario-based discussions.

Scenario 1: Bloc Competition. In this scenario, NATO provides security guarantees to Ukraine as part of a peace settlement, but Russia continues to deepen its ties with China, Iran, and North Korea. The result is two competing blocs, each pursuing advanced nuclear and conventional capabilities. Russia remains determined to divide European allies, and the sustainability of U.S. support is questionable. In this scenario, the United States, Russia, and European states could be incentivized to participate in arms control for economic reasons, such as to free up resources for conventional rebuilding following the war in Ukraine. In scenario-based workshop discussions, experts assumed that Russia will use arms control to buy time and gain a strategic advantage over the United States and its allies, who will struggle to allocate the necessary resources to deter renewed Russian aggression in Europe, particularly due to a U.S. shift toward the Indo-Pacific. Attempts at nuclear arms control, however, will be challenging, as Russia continues to insist on the inclusion of French and British nuclear forces, while the United States similarly demands Chinese engagement.

Scenario 2: Strategic Disadvantage. In this scenario, Russia has achieved a favorable peace settlement in the war in Ukraine and concludes that its nuclear saber-rattling had the desired effect. Moscow plans to continue relying on nuclear weapons for risk manipulation. With the war in Ukraine concluded, the United States shifts its focus away from Europe, and NATO becomes a fractured alliance struggling to uphold its security commitments. As a result, Europe is forced to become ruthlessly pragmatic and efficient in defense investments to fill a potential U.S. “deterrence gap.” Europe has limited leverage to incentivize Russia into arms control, aside from potential economic benefits. However, Europeans remain distrustful of Russia’s intentions and suspect that Moscow would use any arms control as an opportunity to build up its forces and achieve strategic supremacy in the region—potentially including further territorial aggression. In this scenario, there may be opportunities for a U.S.-Russia bilateral agreement, such as a time-limited extension of New START limits or a performative agreement similar to the 2002 Moscow Treaty. In the absence of credible U.S. nuclear guarantees, proliferation pressures increase for U.S. allies, putting the NPT at risk.

Scenario 3: Strategic Advantage. The war in Ukraine ends on terms unfavorable to Russia, forcing Moscow to concede all territory gained since 2022 and weakening its partnerships with China and North Korea. The United States and key European actors provide security guarantees to Ukraine in exchange for its agreement not to join NATO, and the alliance is strengthened through an expanded dual-capable aircraft (DCA) mission and enhanced conventional deterrence. Russia faces economic constraints and political instability, creating opportunities to use economic incentives as leverage for arms control. Additionally, arms control could serve as a “PR win” for Putin by reaffirming Russia’s status as a nuclear peer with the United States while offering a face-saving option for reducing defense spending. In this scenario, NATO is eager for arms control to codify the new status quo and strengthen transparency and predictability. Options for arms control could include bilateral limits on all nuclear weapons—either through a New START follow-on agreement or a Presidential Nuclear Initiatives (PNI)–style agreement—along with recommitting to existing agreements such as the OST; however, the United States will continue to reject any reduction agreements until Beijing participates, and Moscow may take the same stance regarding France and the United Kingdom, though with limited bargaining leverage.

Scenario 4: Disordered Competition. Russia, the United States, and Europe all face economic and domestic political pressures but remain entrenched in their strategic positions. Russia makes a third attempt to seize Ukraine assuming that the United States will not intervene in Europe due to its focus on deterring China. Europe is left to deter further Russian aggression, determine the extent of its support for Ukrainian independence, and coordinate defense planning. In this scenario, arms control could center on crisis communication and risk reduction mechanisms, but options for strategic arms control would be limited. Russia will insist on French and British participation, while Europeans refuse any arms control dialogue as long as Moscow continues to threaten sovereign territories backed by nuclear threats; however, the P5 process could serve as a forum for dialogue to prevent escalation to nuclear use. Another opportunity lies in leveraging existing nuclear treaties and mobilizing the wider international community to uphold the nuclear taboo and pressure all parties to refrain from nuclear escalation.

Scenario 5: Change of Leadership in Moscow. In this first black swan scenario, the war in Ukraine continues into the fall of 2025, but Russian military activity slows following reports that Putin is ill. Eventually, Putin succumbs to his illness and dies, leaving no clear successor. As a result, decisionmaking in Moscow is crippled for months. Ukraine uses this period to strengthen its frontlines and make gains in Donetsk. In this scenario, Russia’s objectives will be driven by a desire to demonstrate the credibility of a new regime, which could include securing a decisive victory in Ukraine and/or securing an agreement with the United States. The new leadership may prioritize stabilizing the economy over defense investments, in which case arms control could serve as a face-saving option for reducing strategic forces. However, it is equally possible that the new regime adopts a hardline approach to shore up its political base within the Kremlin and rejects any Western overtures for dialogue. This scenario is perhaps the most uncertain and least stable of the six, despite repeated expert claims in discussion about other scenarios that “arms control won’t be possible as long as Putin is in the Kremlin.”

Scenario 6: Nuclear Use. In the second black swan scenario, peace negotiations are deadlocked, and Ukraine and Russia reengage in military conflict. Due to renewed European resolve to support Ukraine, NATO members launch a conventional strike on Russian forces in Ukraine, signaling their commitment to the renewed conflict and threatening Russia with a decisive battlefield defeat. In response, Russia detonates multiple sub-kiloton-yield nuclear weapons over a command post and battlefield positions in northern Ukraine, killing thousands of Ukrainian military personnel and allowing Russian forces to break through the frontline, forcing an unfavorable peace settlement on Kyiv. NATO responds conventionally, and the international community expresses widespread condemnation of Russia’s nuclear use. By 2027, however—one year after the detonation—international outrage has faded, the majority of Global South states have normalized relations with Moscow, and China has resumed support for the Russian defense industry. Prospects for arms control are mixed. On the one hand, breaking the nuclear taboo after 80 years of non-use, along with the subsequent humanitarian and environmental consequences, prompts calls for ambitious arms control measures to reduce the risks of further nuclear use. On the other hand, the lack of sustained international outrage and Russia’s argument that nuclear weapons use against a military target was justified under international law when the “existence of the state” was perceived to be at risk could suggest a normalization of nuclear threats and small-scale use. In this scenario, the wider international response could play a decisive role in shaping the prospects for arms control and preventing further nuclear use.

Competitive Arms Control and “Player Europe”

Two main themes emerged across all scenarios: Competition with Russia is likely to continue after the war in Ukraine, and Europe is emerging as a more significant player in deterrence and arms control in the Euro-Atlantic region. While these two trends were evident across all scenarios, two additional insights emerged from the black swan scenarios, aligning with broader findings: A change in leadership in Moscow will not necessarily lead to a breakthrough in arms control, and the nuclear taboo is weakening.

Competition with Russia Might Not End Anytime Soon

A key finding across all six scenarios is that U.S. and/or European competition with Russia is likely to continue after any peace settlement in Ukraine, and Euro-Atlantic security will not revert to the status quo ante. Throughout his rule, Putin has expressed a “persistent sense of vulnerability” and publicly voiced a fear of encirclement. In his 2007 Munich Security Conference speech, he expressed disdain for the U.S.-led global order, saying, “Unilateral and frequently illegitimate actions have not resolved any problems. Moreover, they have caused new human tragedies and created new centres of tension.” Following Russia’s 2014 invasion of Crimea, Putin declared, “we have every reason to assume that the infamous policy of containment, led in the 18th, 19th and 20th centuries, continues today.” Immediately before Russia’s full-scale invasion of Ukraine on February 24, 2022, Putin asserted that NATO’s “main goal is to contain Russia’s development. This is the whole point. In this sense, Ukraine is simply a tool to reach this goal.” Based on our scenario analysis, Russia’s strategic objectives at the war’s conclusion could include continuing territorial advances in former Soviet states to expand a “buffer zone,” attempting further incursions into Ukraine as part of a face-saving strategy, or perceiving a peace settlement favorable to Moscow as acquiescence to Putin’s ambitions.

In all of the project’s scenarios, a peace settlement over Ukraine did not readily facilitate a return to traditional arms control. This was due to enduring distrust in Moscow, Washington, and European capitals, as well as conflicting arms control priorities. Russia has repeatedly violated or suspended participation in arms control agreements. According to former Under Secretary of Defense for Policy Eric Edelman and former National Security Council Senior Director for Defense Policy and Arms Control Franklin Miller, Russia has violated nine major agreements under Putin. They argue, “Given this deliberate and well-documented track record, the bar for holding Moscow accountable for its actions under any agreement it might sign regarding Ukraine’s future, much less the kinds of nuclear arms control agreements in which President Trump has also shown an interest, should be exceedingly high.” Russia’s track record was a key inhibitor of arms control across the project’s scenarios. In most cases, participants feared that Russia would attempt to use arms control both to constrain the West and to gain strategic advantage. For example, Russia could pursue limits on regional missile defenses that would asymmetrically benefit Moscow. In this context, arms control was perceived as a potential tool for undermining strategic stability. In short, the scenario analysis revealed that future strategic stability will likely depend on waiting for—and attempting to deter—the next round of Russian territorial aggression.

None of the scenario discussions indicated that Russia would reduce its reliance on nuclear weapons following the war in Ukraine. In fact, Moscow may be emboldened by the war’s conclusion, viewing its strategy of coercion as successful. Russian nuclear rhetoric evolved in tandem with its activities on the battlefield, beginning with Putin’s threat on the day of the February 24, 2022 invasion: “No matter who tries to stand in our way . . . Russia will respond immediately, and the consequences will be such as you have never seen in your entire history.” Subsequent nuclear signaling included warnings that attacks on illegally annexed Ukrainian territories could trigger nuclear responses, as well as large-scale nuclear exercises, as Russia suffered battlefield losses.

Russia’s rhetoric has been matched by a buildup of its nuclear forces. In congressional testimony, defense expert Austin Long catalogued new Russian nuclear platforms under development, including the SS-X-30 heavy intercontinental ballistic missile and Status-6 autonomous underwater drone. Long also warned that Russia was pursuing a nuclear posture with options that “would include limited nuclear use in dire circumstances. Yet dire circumstances, from a Russian perspective, could occur very quickly in a conflict.” Russia’s nuclear doctrine states that Russia could use nuclear weapons in response to a “critical threat” to its sovereignty. The type of action that would constitute a “critical threat” to Russian sovereignty is ambiguous, however, allowing Moscow to justify nuclear use under a broad range of circumstances. Experts consistently expressed skepticism that Russia would abandon its nuclear trajectory due to a peace settlement: If Russia emerges from the war strategically weaker, it may continue relying on nuclear weapons to compensate; if it emerges stronger, it could be emboldened to double down on its nuclear saber-rattling.

Experts concluded that Russia has a fundamentally different perception of the Euro-Atlantic security environment and what “strategic stability” in that context would entail. Many of their observations from the workshops, which were held under the Chatham House Rule, have been reflected in recent scholarship on the topic. As described by Kristin Ven Bruusgaard, “NATO and Russian policymakers disagree on the key challenges to crisis stability in Europe. NATO policymakers express concern that Russia may consider a direct military attack on NATO as a continuation of the war in Ukraine. Russian policymakers worry that NATO or the West is seeking to undermine the Russian state on its periphery and from within.” The scenarios all pointed to the potential for economic incentives for arms control, but any reductions or limitations with meaningful economic benefits would likely be complicated by enduring distrust, ongoing competition, and the anticipation of strategic instability. Since its invasion of Ukraine in 2014, Moscow has proven somewhat impervious to economic pressure, such as sanctions. Additionally, it appears to have either avoided or disregarded any international reputational costs.

Multiplayer Arms Control

The second main finding of the project was that Europe is playing an increasingly significant role not only in deterrence within the Euro-Atlantic, but also in shaping prospects for future arms control agreements. Scenario-based discussions acknowledged the challenge of defining “Europe” as a geopolitical actor, particularly due to variations in threat perception, domestic politics, and nuclear status. For the purposes of this project, “Europe” primarily refers to European members of NATO, though the term can encompass a complex and diverse mix of states. In all but one of the project scenarios, U.S. and European priorities were not in clear alignment due to the U.S. shift in focus toward the Indo-Pacific and potential domestic political factors. Depending on the outcome of the war in Ukraine and the process by which any peace settlement is reached, U.S. and European objectives may further diverge, leading Europe to consider exploring greater strategic autonomy from Washington. Amid the war in Ukraine, Europe has already demonstrated its importance in conventional military capabilities. Continued investment in the European defense industrial base could ensure that Europe sustains this influence in the long term. The new €150 billion loan plan proposed by the European Commission forces participants to purchase European-made equipment and will ensure that any rapid effort to acquire new capabilities also strengthens the European defense industrial base in the long term. Additionally, France and the United Kingdom have signaled their intent to increase defense spending beyond NATO’s 2 percent target, while Poland is nearing 5 percent.

Numerous experts in the scenario-based discussions pointed to Russia’s insistence that French and British nuclear forces be included in any future agreement. Russian Ambassador to the United States Anatoly Antonov has repeatedly stated that Russia’s priority is to engage France and the United Kingdom in arms control dialogue, particularly “in light of London’s recent decision to increase the maximum level of nuclear warheads by 40%,” referring to the 2021 Integrated Review. In many of the scenarios, however, Europe is expected to prioritize enhancing its conventional and nuclear deterrence capabilities, which could pose a challenge for any arms control initiatives entailing reductions or limitations on capabilities. In some scenarios, Europe appeared positioned to play a spoiler role in strategic arms control.

In addition to the importance of Europe in future arms control, multiplayer arms control is further complicated by the importance of including China’s nuclear forces in any future agreement for Washington. During scenario discussions, participants generated numerous ideas for bilateral arms control, some of which are discussed below, but they were skeptical of their long-term prospects due to the need to include Beijing. The Strategic Posture Commission concluded, “The ideal scenario for the United States would be a trilateral agreement that could effectively verify and limit all Russian, Chinese, and U.S. nuclear warheads and delivery systems.” Additionally, in his February 2025 comments expressing an interest in “denuclearization” and arms control, Trump was explicit that this should include both Russia and China. Thus far, Beijing has rejected attempts at arms control on the grounds of enduring U.S. support for Taiwan and because of an asymmetry in arsenals. For example, in July 2024, China’s Ministry of Foreign Affairs announced that it was suspending upcoming arms control negotiations with the United States over U.S. arms sales to Taiwan. The United States’ focus on incorporating China into arms control will also persist after the end of the war in Ukraine.

Black Swans: Don’t Wait for a Gorbachev Moment, and the Nuclear Order Is Wobbly

One surprising finding from the scenario analysis was that prospects for arms control are seemingly personality agnostic. In the black swan scenario, wherein Putin dies and there is a leadership change in Moscow, arms control opportunities did not flourish, at least in the 2027 timeframe. Workshop participants pointed to the political leadership surrounding Putin, which would likely produce his replacement and share his worldview. Putin’s successor may be able to provide top-down support for rapprochement and arms control, but they would likely first need to consolidate power among traditional hardliners, build trust with U.S. and European counterparts, and surround themself with like-minded policymakers to execute their vision, as occurred in the case of Mikhail Gorbachev. An additional challenge would be reshaping public attitudes in Russia toward the West to facilitate rebuilding trust. In terms of arms control, this finding from the scenario-based discussions doesn’t rule out any potential agreements but suggests that they would likely be performative in the short term. In many ways, this finding challenges conventional wisdom that a change in leadership can produce arms control breakthroughs, such as the arrival of Gorbachev in the 1980s, and recommends a more sanguine approach to the influence of personality, even in authoritarian regimes, over arms control in the short to medium term.

The second black swan scenario produced an equally pessimistic conclusion in terms of prospects for future arms control. In a scenario of nuclear use, the international community succeeded in the short term but failed in the long term to hold Russia accountable, with dangerous implications for both the nuclear taboo and the wider nuclear order. The arms control architecture is now a shell of its former self. Russia has systematically undermined the practice of bilateral strategic arms control because it believes such agreements no longer serve its interests and, according to Russian Foreign Minister Sergey Lavrov, the United States’ interest in arms control is based on an attempt “to try to establish control over [Russia’s] nuclear arsenal and minimize nuclear risks for itself.” Additionally, the nuclear order is crumbling, and long-standing pillars of the regime, such as the NPT, risk sliding into irrelevance due to a failure to reach consensus, along with a muted international response to Russia’s nuclear saber-rattling. To be clear, the NPT does not appear to be at risk of some dramatic collapse sparked by a cascade of withdrawals; rather, it risks a gradual descent toward a hollow treaty that is still in force but lacking in political buy-in. The end of the war in Ukraine will not suddenly revive the nuclear order, so this wider challenge for arms control agreements such as the NPT and the Comprehensive Test Ban Treaty (CTBT) will also remain.

A final finding came primarily from next-generation experts, who posed fundamental questions about the enduring value of institutions. One participant posed the question, “How hard should we fight” to keep institutions like the NPT, but also NATO? This also reflected a geographic difference among participants, with European experts focusing on how to keep the United States engaged in NATO and preserving the alliance, whereas U.S. participants were more focused on the two-peer challenge and balancing deterrence in both Europe and the Indo-Pacific. Next-generation experts offered a creative vision for finding a balance between preserving existing institutions and pursuing new, more inclusive approaches to security and arms control, such as formalizing the role of the private sector or civil society organizations in traditional diplomatic forums. This finding not only offers a valuable framing for the future of arms control—what is worth saving?—but also demonstrates the value of cross-generational and early-career engagement in discussions about seemingly intractable security and defense challenges.

“Integrated Arms Control” in Practice

In January 2022, CSIS published a report on integrated arms control that advocated for a more flexible approach to arms control to address a rapidly changing security environment. The report outlined a “menu of options” for pursuing arms control in an era of strategic competition, allowing for flexibility in format, verification, membership, and limits. This adaptability would enable arms control strategies to accommodate new agreements, adopt different modalities, or modify existing agreements. The end of the war in Ukraine could present an opportunity to apply the report’s concepts and draw from its menu of options to develop new arms control opportunities and a refreshed arms control agenda.

But arms control is not the only tool for strengthening deterrence. For decades, scholars and policymakers have emphasized the need to broaden the concept of strategic stability to account for nonnuclear capabilities, as well as broader political factors and capabilities that are not easily quantifiable, such as emerging technologies like cyber. An overarching finding from this project is that strategic stability must also expand to encompass a wider range of actors; it is no longer a purely bilateral equation—if ever it was. Both China and “player Europe” will shape the strategic environment and have the potential to strengthen strategic stability through various tools, including arms control; however, it is worth remembering that arms control is but one tool for strengthening the condition of strategic stability and avoiding escalation to nuclear use. Other critical tools include deterrence and norms, which should also be considered in crafting new policy approaches.

A Return to U.S.-Russia Strategic Arms Control?

In most scenarios, there was no clear overlap in Russian or U.S. and European strategic objectives in arms control, nor in the capabilities they would want to see captured in any agreements. Moscow has indicated that it would want to see limits on nonnuclear capabilities, including long-range precision strike systems and missile defenses. An enduring Russian priority for decades has been to incorporate British and French nuclear forces into any future agreement, counting them toward “parity.” From the U.S. and European perspectives, the goal of future arms control agreements ranged from specific to conceptual. A primary specific interest was limiting and reducing Russian tactical nuclear weapons (TNWs). A 2024 State Department report on Russian TNWs stated that the United States “seeks to address Russian [nonstrategic nuclear weapons]” due to their ability to “alter the nature of a conflict, create the potential for uncontrolled escalation, and have strategic effects.” Other priorities could include re-establishing a commitment to existing agreements such as the OST and the CTBT. Broader objectives could include reestablishing transparency and implementing Transparency and Confidence-Building Measures (TCBMs) with Russia to improve predictability regarding the trajectory of its strategic forces.

Realistically, treaty-based strategic arms control options may be extremely limited across the scenarios due to the crucial role of third parties. The United States will likely reject any nuclear arms control agreement that excludes China, while Beijing has maintained that it will not engage in negotiations as long as Russia and the United States possess substantially larger arsenals. A further complication arose in 2024 when China halted arms control consultations over U.S. arms sales to Taiwan, adding yet another hurdle to U.S.-China engagement on the issue. Similarly, Russia may continue to reject any nuclear arms control agreement that does not include European actors. Even within these constraints, however, opportunities for arms control may still exist.

One option might be for the United States and Russia to seek an agreement to continue abiding by the New START limits of 1,550 deployed warheads on 800 strategic delivery vehicles for up to three years. This would allow time for the lengthy and detailed process of negotiating a new strategic arms control agreement that includes additional actors. The agreement could be established through presidential directives, reflecting the increasingly close relationship between Trump and Putin. Such an agreement would have to rely on national technical means for verification but could also set up a standing arms control dialogue to provide transparency into the agreement’s implementation and explore opportunities for a more permanent, long-term agreement.

On the one hand, an agreement to abide by the limits set by New START could create momentum for a follow-on agreement and reduce the pressure to engage in an arms race on specific strategic systems. On the other hand, New START only limits strategic systems, meaning many of Russia’s most threatening systems in the eyes of Europe—such as novel and dual-use nonstrategic delivery vehicles like the Kh-47M2 Kinzhal air-launched ballistic missile—would likely remain unrestricted by any arms control treaty. Furthermore, while ensuring parity between Russian and U.S. strategic forces contributes to broader strategic stability, much of the treaty’s value lies in its extensive and invasive verification regime, which would be lost in a simple agreement to abide by its limits.

Another option discussed in the scenarios was a performative arms control agreement, similar to the 2002 Moscow Treaty. Such an agreement might set an overall ceiling limit while allowing both the United States and Russia to determine their own strategic and sub-strategic limits. It could be negotiated relatively quickly, without verification, and with little or no engagement with allies. Such an agreement, however, would come with risks, including failing to account for Chinese strategic capabilities and, given Russia’s track record, potentially leaving the United States vulnerable to the consequences of Russian violations. A particular fear among Europeans is that the United States might grant Russia a sphere of influence in the Euro-Atlantic region as part of any arms control agreement.

Prior to any agreement, the United States will need to prepare to hedge. Specifically, it should enhance its nuclear deterrent by preparing to upload warheads if Russia no longer observes New START central limits, expanding capacity in the National Labs, and developing additional delivery platforms, to include nuclear sea-launched cruise missiles and a new standoff capability. In the past, the United States has created negotiating leverage by strengthening its conventional, nuclear, and missile defense capabilities to incentivize arms control engagement. A key advantage of many of these measures is that they can be paused or rolled back in the event of a breakthrough in arms control, providing both negotiating leverage and enhanced deterrence. If the United States can build leverage and offer opportunities for arms control engagement, the ball would remain in Moscow and Beijing’s court.

Player Europe, Strategic Stability, and Arms Control

Europe is getting its house in order. For now, Europe seems relatively united in its objectives of deterring further Russian aggression in the region, though the specific means and sustainability of this approach are still being worked out. The real first step for Europe must be to develop a new strategy for deterrence, accounting for uncertainty in its relationship with the United States. This strategy will need to address a key question: How much strategic autonomy does Europe want vis-à-vis the United States? At one end of the spectrum is a relatively extreme form of autonomy, potentially including more independent nuclear capabilities (discussed in greater detail below), which may appeal to France and some Eastern European countries that feel the threat from Russia most acutely. At the other end is a hedging approach, in which European states maintain close relations with Washington—potentially on a more bilateral basis—while building the capacity and flexibility to act independently should the need arise. The relationship between the United States and the United Kingdom, for example, has withstood the test of time and historical challenges and should remain a priority on both sides of the Atlantic.

A divide between the United States and Europe comes with significant risks. Greater strategic autonomy for Europe could lead to states unilaterally escalating with Moscow—either unintentionally or intentionally—such as by launching attacks inside Russia, whether kinetic or non-kinetic. This approach would be highly dangerous, as it could pull the continent into an uncoordinated and unwanted war while also carrying significant implications for the United States.

Alternatively, a reliance on bilateral alliances and a hedging approach could fracture European coordination in deterring Russia or leave the continent vulnerable to further aggression. This report does not offer a specific recommendation for where Europe should position itself on this spectrum of autonomy. Instead, it recommends that key European actors work together to develop a coherent strategy that enhances deterrence, allows for flexibility in the event of a U.S. withdrawal, and simultaneously strives to maintain strong ties with Washington, given the legacy of cooperation and the tangible benefits it has provided for European security.

One recommendation that fulfills all of these objectives is for European states to continue increasing defense spending and coordinating their defense industrial bases. Europe could adopt a “comparative advantage” approach to defense planning by designating lead nations for specific defense investments and capabilities. For example, if one European country proves particularly efficient at producing drones, it should prioritize that capability, while another country that excels in munitions should focus on munitions production. Additionally, Europeans would need to make major investments to compensate for any withdrawal of U.S. conventional capabilities. For instance, most of NATO’s intelligence, surveillance, and reconnaissance (ISR) capabilities rely on the United States, and Europe has yet to develop comparable capabilities. Ideally, this type of coordination could be conducted as part of NATO’s defense planning efforts.

One key consideration for a new European defense strategy concerns independent nuclear forces. While the United States remains committed to its extended deterrence obligations to its allies, recent political shifts have prompted conversations in Europe about the credibility of that deterrent. France has been the most vocal of the European nuclear-armed states in openly discussing the concept of a European extended deterrence, with French President Emmanuel Macron repeatedly indicating his willingness to engage in such discussions with European allies. Statements from leaders in France, Germany, and Poland suggest that, in the absence of a credible and strong U.S. extended deterrent, they would be interested in pursuing additional nuclear capabilities—either through a European deterrent or independent nuclear weapons programs. Europe’s conventional investments, along with French proposals to expand its nuclear deterrent to include other European states, could complicate strategic decisionmaking for Russia. Options for enhancing European-led nuclear deterrence could include expanding French and British nuclear forces—such as adding an air leg to the British deterrent—or France becoming an observer in the NATO Nuclear Planning Group. As argued by CSIS experts Sean Monaghan and Doreen Horschig, however, debates about a European nuclear deterrent are a distraction from the real priority: strengthening conventional deterrence through increased combat power. The best option remains the continuation of a credible U.S. extended nuclear deterrent, both to prevent nuclear proliferation and to strengthen the NPT—a position that was universally acknowledged among U.S. and European workshop participants.

As part of its new strategy, Europe may also decide to develop a new arms control policy. Historically, European states have not been in perfect alignment on arms control. Countries in Eastern Europe and the Baltic states are typically skeptical of arms control, while Germany and the Netherlands are more positive, and France has historically focused its arms control efforts on the NPT, for example. But now, Europe can make or break future arms control efforts, whether that involves a new nuclear reductions treaty or conventional arms control, and it will cast a shadow over strategic considerations and balancing, especially for Moscow. A priority for the new arms control strategy should be flexibility, such as through time-limited agreements or the freedom to mix and match forces, or more informal approaches, like risk reduction measures within the P5 process. One specific opportunity might be a three-year limit on warheads in partnership with China, whereby the combined British and French nuclear forces, along with China, do not exceed a certain ceiling. Verification would rely on national technical means and open-source intelligence, so confidence in the agreement could be limited. It could provide some degree of predictability and gradually bring China into arms control dialogues. To be clear, the authors recognize that this proposal is highly unlikely not only because of China’s traditional position on arms control, but also due to France’s insistence on maintaining independence and not imposing constraints on its nuclear forces. Nonetheless, an openness to such discussions could increase pressure on Beijing and demonstrate an enduring commitment to arms control and the NPT on the part of Europe’s nuclear powers.

Conventional arms control will also need to be a consideration in a European arms control strategy. European states remain committed to the Vienna Document, which provides a useful forum for information exchanges and transparency in conventional capabilities. The Vienna Document could prove particularly valuable in monitoring any ceasefire or peace settlement in Ukraine. A creative option, recently suggested by RAND, would involve geographic limits on conventional capabilities—specifically, limits “based on the geography of activities and deployments and perceived vulnerabilities” rather than explicit numerical caps on certain forces. The report suggests that “The sides could also agree to voluntary but coordinated self-restraint on naval and air activities in the Black and Baltic Seas and in the High North.” There are several reasons why Russia and Europe may have a common interest in geographical limits on the deployment of certain systems or activities. Russia has repeatedly linked its perception of strategic stability to the existence of a geographical buffer zone between itself and NATO. Limits on deployment locations, rather than numbers, would allow Europe to continue working toward qualitative and quantitative conventional superiority vis-à-vis Russia. This geographic approach, however, could exacerbate divisions within Europe because of different threat perceptions between Northern, Eastern, and Western European states. Such an agreement could leave one or more members of the alliance feeling left out in the cold.

Risk Reduction in the P5 Process

Despite its challenges, the P5 process remains the best game in town for dialogue on risk reduction and laying the groundwork for multilateral strategic arms control. Established in 2009 as a signal that the P5 countries took their disarmament commitments under the NPT seriously, the P5 process has hosted a number of arms control proposals, including a missile launch notification regime, transparency into former nuclear test sites, and a formalized crisis communication channel between P5 capitals. While these have had limited success, the end of the war in Ukraine could provide a new impetus for such risk reduction efforts. An additional benefit of this approach will be the strengthening of the NPT in the process. There are at least three opportunities for the P5 process to advance arms control following the war in Ukraine.

First, during the war in Ukraine, Russian military leaders apparently considered following through on their nuclear threats, bringing Europe closer to the nuclear brink than at any point since the Cold War. The war in Ukraine, therefore, should offer unique lessons for nuclear risk reduction efforts and crisis communication. The P5 should launch a Crisis Stability Initiative as a standing agenda item to first review the sources of instability during the war in Ukraine and perceptions among all parties about risks of nuclear use. The initiative should then identify tools for reducing these risks in the future by engaging a wider group of experts from nonnuclear weapon states, nongovernmental organizations, and next-generation researchers. This engagement-based approach can produce creative solutions, removed from many of the practical and political constraints of the P5 process itself, but then be tailored to the P5’s preferences.

Second, based on the new Crisis Stability Initiative, the P5 could agree to a shared set of responsibilities and commitments to communicate and reduce the risks of misperception during a crisis. This might include a wider and renewed commitment to “hotlines” across all P5 members. These commitments could be included in the P5 deliverables to the NPT review process, further strengthening the nuclear order as a result. If such an initiative is too ambitious for the P5, an alternative would be a Track 2 dialogue or leveraging the P5 Track 2 and/or Young Professionals Network to identify potential shared commitments.

A final step would be for the P5 to expand their use of the common reporting form. As Mike Albertson, deputy director of the Center for Global Security Research, has argued, one of the greatest benefits of arms control is information exchanges. The common reporting form is a unique opportunity for such exchanges and would be particularly important in further socializing China with transparency building. China has become more involved in these efforts in recent years. In November 2024, for example, Chinese President Xi Jinping signed a joint understanding with then-U.S. President Joseph R. Biden Jr. to keep “human control” in nuclear decisionmaking. France and the United Kingdom have made similar statements, and Russia is the only member of the P5 refusing to make a “human in the loop” statement. Additionally, both the United States and China have notified one another of missile test launches, despite no formal agreement to do so. Continuing this trajectory with the common report form will be an important contribution to future arms control opportunities and again contribute to the NPT review process.

Strengthening the Nuclear Order

Next-generation experts asked the question, “What is worth fighting for?” among existing institutions. While it is tempting to say “all of it,” especially with regard to the nuclear order, that may be a challenge given the demise of traditional arms control tools in recent years. At least three treaties, however, remain and are worth a focused multilateral effort to maintain and strengthen: the NPT, the CTBT, and the OST. These treaties are important not only because they are some of the last remaining mechanisms with widespread international participation, including by nuclear possessors, but also because they are the foundation of nuclear norms. The NPT continues to have constraining power over nuclear proliferation, as withdrawal would likely come with extreme political and economic costs, as witnessed in the case of North Korea. This restraining power could be tested in the coming months and years, both because of Iran’s continued nuclear activities and increased enrichment, and because of concerns about allied proliferation in the face of questionable U.S. credibility. Maintaining the CTBT will not only strengthen the norm against a return to nuclear testing, which would include massive humanitarian and environmental consequences, but also slow the vertical proliferation of nuclear arsenals, especially in China. Finally, recent allegations against Russia highlighted the potentially catastrophic consequences of deploying a nuclear weapon in space, which could hold at risk international communication systems and the functioning of critical infrastructure in the United States and Europe. The OST is one of the best tools for pressuring Russia to refrain from such a move, but it requires a more robust international response.

The Global South or Global Middle Ground is poised to play an influential role in the arms control agenda and in upholding these treaties and norms. In addition to calling on all states to continue to observe existing treaties, these countries can take additional steps to strengthen the nuclear taboo and other nuclear norms. The Treaty on the Prohibition of Nuclear Weapons (TPNW), for example, currently has 73 full members and 94 signatories, and the treaty bans the threat of the use of nuclear weapons. While TPNW efforts to date have focused on the weapons themselves, resulting in a blanket approach that treats all nuclear possessors the same, a more targeted approach to norm-building—one that explicitly calls out bad behavior, such as threatening nuclear use as part of an illegal invasion—could both increase pressure on norm violators and strengthen the international order. States Parties to the TPNW should issue a joint statement in NPT forums condemning the role of nuclear threats in Russia’s war in Ukraine and stop treating all nuclear possessors as a monolith. Rather, they have a unique and powerful opportunity for strengthening strategic stability and reducing future nuclear risks by upholding norms of non-use.

The Coming Instability

This report has identified numerous opportunities for arms control after the war in Ukraine that prioritize enhancing deterrence and flexibility; however, these come with a host of challenges. First and foremost is the risk of an arms race, given that a buildup in U.S. and/or European conventional and nuclear forces could be perceived as escalatory by Moscow or Beijing. Not all buildups are created equal, of course, and not all buildups equate to an arms race. The risks associated with a buildup depend on its scale, speed, and perception. The buildups the authors recommend, therefore, should be accompanied by robust analysis of how they would be perceived by adversaries, inspiring risk reduction efforts to avoid escalation and falling into an action-reaction cycle. A related risk is groupthink: While this report has captured the overwhelming consensus of scenario-based discussions, there were occasional dissenters who suggested that Russia might change its course after a peace settlement in Ukraine. And while many of the report’s recommendations for enhancing deterrence can be scaled back in the event of rapprochement, they could be perceived as a lack of seriousness about arms control and inadvertently undermine dialogue or opportunities for cooperation, potentially becoming self-fulfilling prophecies. That is not in any way the authors’ intention, and above all, the authors recommend that the United States and Europe remain open to arms control opportunities and be prepared to capitalize on them when they present themselves.

Another challenge will be overcoming historical positions on what and who to include in arms control. While this report encourages flexibility in agreements to allow for hedging, some arms control positions may prove to be too entrenched to allow even short-term cooperation or dialogue. For example, missile defense has historically proven a sticking point in U.S.-Russia arms control negotiations and may be again. In reaction to the establishment of an Aegis Ashore battery in Poland in 2024, Russia lamented that U.S. missile defenses in Europe “leads to undermining strategic stability, increasing strategic risks and, as a result, to an increase in the overall level of nuclear danger.” To take another example, the above analysis demonstrates that European nuclear states could have leverage in negotiations with Moscow, which has repeatedly called for their inclusion in future agreements. But just because European nuclear states have leverage does not necessarily mean that they should, or are willing to, use it. In the era of competition, enhancing deterrence vis-à-vis Moscow will likely remain a priority, and Europe may choose to reject arms control altogether.

Coordination and unity within Europe will also be a challenge, particularly with regard to resourcing if European states refuse to raise taxes, cut domestic programs, or borrow money. Enhancing conventional and nuclear deterrence and generating leverage in arms control will require an unprecedented level of coordination among these states, particularly with regard to defense investments. The large, but not perfect, overlap between the two largest multilateral groups with the potential to shape European defense investment—the European Union and NATO—will require close coordination on the margins and a clear division of labor for all of Europe. Finding the resources to make these investments will be asymmetrically challenging for smaller European states and may require Europe to consider increasing its borrowing, taking drastic fiscal measures, or developing unprecedented coordination to increase efficiencies. A coordinated European position on arms control will also be a challenge, given historically divergent positions between Eastern and Western European states.

Despite these challenges, Euro-Atlantic stability is on the line. Many states in Europe perceive the coming years as decisive in determining whether Putin’s ambitions are checked and whether or not nuclear weapons are used. Putin has demonstrated that he is not someone to be trusted, so any future promises or arms control agreements should be accompanied by hedging and continued commitments to enhance deterrence in Europe. European states appear ready to lean in on deterrence and defense, and, as the authors argue, arms control should be part of a renewed competitive European strategy. Arms control remains a crucial tool for strengthening strategic stability and reducing the risks of nuclear use. The game is now on to develop new arms control solutions for an era of competition, and for Europe to step into a leading role.

Appendix A

Six Scenarios for 2027

Scenarios 1–4 were based on an alternative futures approach with variation in alliance unity and adversary capabilities.

▲ Table A-1: Scenarios for Euro-Atlantic Security

The additional two scenarios are black swans, included to account for significant developments that could shape the future of arms control but were not covered in the alternative futures. Each scenario was analyzed to identify (1) Russian, U.S., and European strategic objectives; (2) potential points of leverage to incentivize Russian participation in arms control; and (3) specific arms control outcomes that could result from each scenario. Below is the scenario text provided to workshop participants, along with a summary of discussion points.

SCENARIO 1: BLOC COMPETITION

The war in Ukraine ends through a negotiated settlement. Russia cements its control over the territory it occupies as of December 2024. The United States and its allies provide Ukraine with security assurances in the event of future aggression, and Russia offers written negative security assurances. Ukraine renounces its aspiration to join NATO. Cooperation among U.S. adversaries deepens to include formalized technology transfers and increasingly large and frequent joint exercises, sometimes involving nuclear-capable delivery systems. Enhanced cooperation enables Russia and China to expand their diplomatic and economic inroads in Latin America and Africa. Russia, China, and North Korea announce a trilateral arrangement to develop and share technologies related to nuclear submarines. Iran declares that it has constructed a nuclear weapon but will remain in the Nuclear Non-Proliferation Treaty (NPT). The United States remains committed to NATO and its Indo-Pacific allies. The Trump administration maintains the United States’ existing agreements as of December 2024, including AUKUS, the Nuclear Consultative Group, and NATO. The United States, its allies, and its adversaries seek to rapidly expand their defense capabilities, leading to an arms race and a large military buildup on all sides. Both blocs make advances in potentially destabilizing delivery system technologies, including theater-range, dual-capable systems. European allies make limited progress in implementing a continental air and missile defense system, with some allies further ahead than others. U.S. nuclear modernization proceeds according to schedule.

Strategic Objectives: In this scenario, Russian objectives could include a desire to buy time to rebuild its forces and make another attempt at seizing Ukrainian territory or elsewhere in the former Soviet space. Moscow does not appear to have learned a lesson on the value of cooperation from the war in Ukraine, and there have been no other signs that Russian President Vladimir Putin’s wider strategic ambitions have abated. As a result, Russia’s strategic objectives also include continuing to attempt to divide the United States from its European allies, such as through ongoing disinformation campaigns and gray zones attacks on NATO members, and continuing trends set by Russian cyber operators like COLDRIVER, which seek to leak potentially disruptive political information to sow political unrest in rival states. Perhaps ironically, one of Russia’s strategic objectives may be in perfect alignment with Washington’s in this scenario: a shift in U.S. resources from the European to Indo-Pacific theaters. For the United States and Europe, there are shared objectives of focusing on domestic stability and balancing budgets. For Washington, this will mean encouraging more burden-sharing with allies, such as increased conventional capabilities; however, European allies may have a contrary objective of limiting defense spending.

Incentives and Opportunities for Arms Control: In terms of arms control leverage, one of the best tools for incentivizing Moscow to participate in arms control in this scenario could include economic factors and relief, so as to avoid a costly arms race. This would not only free up resources for Moscow to rebuild conventionally following the war in Ukraine but also pause Western buildups, giving Russia an opportunity to attempt to gain some strategic advantage. One particular limitation for the United States in this scenario, based on statements by the previous and current Trump administrations, will be the importance of including China in any future strategic arms control limitations, as the current administration seems to be picking up where the previous administration left off, with its current position nearly identical to the one put forward by president Trump in 2020, when he called for arms control that “includes not only Russia, but also China.” To summarize, in this scenario experts assumed that Russia will be using arms control to buy time and gain strategic advantage over the United States and its allies, which will be struggling to devote the necessary resources to deterring renewed Russian aggression in Europe, particularly because of a U.S. shift to the Indo-Pacific.

SCENARIO 2: STRATEGIC DISADVANTAGE

The war in Ukraine ends through a negotiated settlement that advantages Russia. Ukraine officially cedes the Donbas and Crimea, along with much of Kherson, Kharkiv, and Zaporizhzhia Oblasts. Western leaders warn Russia against further aggression in Ukraine but offer no formal security guarantees. Russia imposes limits on the size of Ukraine’s military and forces Ukrainian President Volodymyr Zelensky out of power. Following the conclusion of the war, Russia begins to amass troops in Transnistria, on the border with Moldova. North Korea successfully tests a new nuclear warhead design, which it developed in partnership with Russia. Russia deepens its cooperation with China and Iran on disinformation efforts targeting the United States and its allies. The Trump administration hints repeatedly that it will withdraw from NATO unless allies increase their defense spending to 3.5 percent of GDP. The Trump administration maintains U.S. participation in AUKUS but withdraws from the Nuclear Consultative Group and considers downsizing the U.S. nuclear mission. U.S. allies face heated internal debates about defense spending; some hold defense spending constant, while a handful move toward anti-nuclear positions. The Netherlands considers joining the Treaty on the Prohibition of Nuclear Weapons. U.S. nuclear modernization falls behind schedule, with the Sentinel and Columbia programs experiencing multiyear delays. Russia rapidly fulfills its planned conventional military expansion, while Europe struggles to keep pace due to funding constraints and coordination challenges. Europe’s defense industrial base stagnates.

Strategic Objectives: Having achieved a favorable peace settlement after the war in Ukraine, Russia’s strategic objectives in this scenario would likely include continuing to advance its regional ambitions and maintaining pressure on NATO so as to further divide Washington from its European allies. Moscow, and others, may take away a lesson from the war in Ukraine that nuclear bullying deterred Western intervention and divided allied support for extended nuclear deterrence. They may continue to rely on this strategy in pursuing other regional aggression, such as in Moldova or Georgia. With the war concluded, the Trump administration feels free to shift capabilities and focus to the Indo-Pacific, largely leaving the Europeans to deter for themselves and work out internal disputes. European strategic objectives thus include preserving the alliance, strengthening regional deterrence and security without U.S. conventional support (with the long-term prospects for extended nuclear deterrence in question), and balancing domestic pressure to cut defense spending now that the war in Ukraine has officially concluded. In this scenario, European states will have to become ruthlessly pragmatic and efficient: They will need to fill the U.S. conventional “deterrence gap,” coordinate their defense industrial bases, and decide how to maintain and strengthen extended nuclear deterrence.

Incentives and Opportunities for Arms Control: Leverage over Russia will likely be limited in this scenario due to U.S. disinterest in Europe and the shift of resources and focus to the Indo-Pacific. The best option for leverage would be a European conventional buildup, along with an increased British and French nuclear presence and commitment to deterrence. For example, if France joined the Nuclear Planning Group and/or extended a nuclear “umbrella” over states in Eastern Europe, including Ukraine, this could slow Russian ambitions in the region and force Russia to the negotiating table to avoid a costly arms race and dangerous standoff. Russia would likely insist on French and British forces being included in any nuclear agreement. As Russia seeks to rebuild conventionally, Europe could also have economic leverage, depending on what happens to seized Russian assets.

SCENARIO 3: STRATEGIC ADVANTAGE

The war in Ukraine ends through a negotiated settlement that favors Ukraine. Ukraine legally cedes Crimea without officially conceding the Donbas, most of which remains under Russian occupation. Russia cedes the other territory that it seized since its full-scale invasion on February 24, 2022. The United States and key European allies provide strong security guarantees in the event of future Russian aggression, and NATO commits to admitting Ukraine into the alliance by 2035. Cooperation between U.S. adversaries largely ends following the conclusion of the war in Ukraine. Russia provides no additional support to the Iranian and North Korean nuclear and missile programs, and Russia’s “no limits” partnership with China produces no meaningful outputs. The United States remains actively engaged in NATO and with its allies in the Indo-Pacific. There are no significant changes to the United States’ global force posture. NATO expands its conventional superiority over Russia, which faces economic troubles and struggles to rebuild and expand its conventional forces. The United States expands the NATO DCA mission.

Strategic Objectives: Rebuilding the Russian economy and ensuring domestic stability would likely be Moscow’s primary strategic objective in this scenario. If Russia chooses to continue pursuing its regional ambitions, it will need to rebuild conventionally and/or increase reliance on nuclear weapons, but will have limited resources for doing so. Another objective will be face-saving for the Putin regime following a less-than-favorable outcome of the war that cost hundreds of thousands of Russian lives. For the United States and Europe, one of the objectives will be pursuing an arms control agreement that codifies the state of play, limiting a return to conventional and nuclear competition in the Euro-Atlantic region.

Incentives and Opportunities for Arms Control: This scenario offers the best prospects for arms control, whereby Russia could use arms control negotiations to demonstrate its great power status and parity with the United States, while also achieving cost savings that would allow it to focus on rebuilding the economy and domestic stability. Interestingly, even in this scenario, many of the workshop participants still doubted that Russia would give up its territorial ambitions in the region and thought that it could actually feel more encircled because of the outcome of the war. The short term, therefore, could prove to be a favorable environment for cooperation; but over the long term, the risk of a return to competition would remain. Arms control options for this scenario could include U.S.-Russia limits on tactical nuclear weapons either through a treaty or Presidential Nuclear Initiatives–style agreement, a new version of a Conventional Armed Forces in Europe Treaty, along with informal risk reduction measures such as a joint commitment to maintain a “human in the loop” in nuclear decisionmaking, exercise and training notifications, and a recommitment to existing agreements such as the Outer Space Treaty. Assuming the United States maintains its position that China must be included in any strategic nuclear arms control, even in this scenario there would be limits on the ambition of an agreement.

SCENARIO 4: DISORDERED COMPETITION

The war in Ukraine ends in a settlement similar to that in Scenario 1, but Russia violates the agreement after a year in a renewed invasion, which quickly settles into a grinding stalemate. The West, facing economic constraints and flagging public support, fails to uphold its loose security guarantees to Ukraine. In response, Ukraine covertly initiates an indigenous nuclear program, which both Russia and the United States quickly discover. After the initial peace settlement in Ukraine, cooperation between U.S. adversaries largely ends. This cooperation remains limited despite Russia’s renewed invasion. Russia provides no additional support to the Iranian and North Korean nuclear and missile programs, and its relationship with China produces no meaningful outcomes. Ayatollah Ali Khamenei, the supreme leader of Iran, dies, leading to a pro-democracy movement that drives a wedge between Russia and Iran. The Trump administration remains in NATO but significantly scales back U.S. participation and activity in the alliance. The administration makes it clear to both adversaries and allies that its primary focus is China and the Indo-Pacific. U.S. nuclear modernization falls behind schedule, with the Sentinel and Columbia programs experiencing multiyear delays. Russia faces economic challenges and struggles to rebuild and expand its conventional forces. European allies, facing similar challenges, struggle to expand the European defense industrial base. Meanwhile, U.S. and Russian nuclear modernization efforts face delays, while China rapidly expands and modernizes its nuclear force.

Strategic Objectives: Russia, the United States, and Europe would all be facing economic and domestic pressure to de-escalate in this scenario; however, they may also be deeply entrenched in their positions. Russia’s objectives would include decisively defeating Ukraine on its third attempt at invasion and could include perceiving the U.S. shift away from Europe as a sign of success in its approach, if not tacit consent. Economic pressures and the continued loss of Russian troops put time pressure on Moscow to secure a decisive victory. For Washington, strategic objectives would include deterring China from starting an opportunistic war while Russia stirs up mischief in Europe, particularly as 2027 is the year Chinese President Xi Jinping indicated China should be prepared for a full-scale invasion of Taiwan. Europe’s strategic objectives would be deterring further Russian aggression and supporting Ukraine in winning the war and pushing back Russia, including through the provision of advanced conventional weapons and, potentially, European troops on the ground.

Incentives and Opportunities for Arms Control: In this scenario, leverage and prospects for arms control would likely focus more on crisis communication and risk reduction. For the United States, any nuclear arms control efforts would need to include Beijing, which would limit opportunities for treaties or strategic arms reductions or limitations in the scenario given the heightened tensions between Washington and Beijing. A key priority for all states would be avoiding escalation to nuclear use and the risk of a nuclear exchange over the outcome of the war in Ukraine. European capitals could appeal to Moscow and Washington to recommit to crisis communication channels and utilize the P5 process to increase transparency regarding threat perceptions and nuclear doctrine amid the ongoing war. Another opportunity would be leveraging existing nuclear treaties and engaging the broader international community to uphold the nuclear taboo and pressure all parties to refrain from nuclear escalation.

SCENARIO 5: CHANGE OF LEADERSHIP IN MOSCOW

In the spring of 2027, rumors spread across Europe that Putin is critically ill. The Kremlin does not respond; however, weeks of Russian inaction on the front lines of Ukraine and signs of intense activity within the Kremlin alert European countries that this time, the rumors may be more credible. Sensing an opportunity, Ukraine begins moving troops and matériel to support a second incursion into Kursk Oblast. Since Trump’s return to office, an uneasy peace agreement has kept the front lines of the war in Ukraine frozen in place since February 2025. Nearly two weeks after the rumors first circulate, Russian state media announces Putin’s death and the appointment of a temporary president. Elections for Putin’s successor are scheduled to take place in 14 days—exactly one month after the initial rumors of his death. Public support appears to be split among several status quo candidates, with no reformist contenders making it to the final rounds of voting, but a pro-war hardliner emerges as the winner. What at first appears to be a rapid and smooth transition of power quickly unravels amid allegations of fraud and electoral interference. A schism rapidly forms within the siloviki, who debate whether to double down on reopening the front in Ukraine or prioritize rebuilding the economy. Russian political decisionmaking is paralyzed for nearly a month, allowing Ukraine to expand its territorial gains in Kursk. As the dust settles in Moscow and the new leader consolidates power by mid-summer 2027, the Kremlin vows that “the Nazi regime in Ukraine and their co-conspirators in the West will pay an unimaginable price for meddling in the affairs of Russia” and declares that the Kursk offensive was “designed to take advantage of Russia at its most vulnerable.”

Strategic Objectives: For Russia, strategic objectives in this scenario would include solidifying the credibility of the new regime, which could involve securing a decisive victory in Ukraine and demonstrating a continued hardline stance to domestic political audiences. Washington may view the change in leadership as an opportunity for arms control, including efforts to ensure the security of Russian TNWs. European strategic objectives could include attempting to build a more favorable relationship with the new leadership in Moscow while preventing any major territorial ambitions or advances. However, they would also likely continue to prioritize a Ukrainian victory, leading European states to seize the opportunity to increase aid to Ukraine.

Incentives and Opportunities for Arms Control: This scenario could present unique opportunities for arms control. The new leadership in Moscow might view high-level arms control dialogues as a means to showcase regime stability and assert its role on the global stage. It may also take a different approach from Putin and prioritize stabilizing the economy over defense investments, in which case arms control could serve as a face-saving option for reducing strategic forces. Experts considered it to be just as likely, however, that the new regime will commit itself to a hardline approach to consolidate its political base within the Kremlin and reject any Western overtures for dialogue. One surprising finding from this scenario was that prospects for arms control appear to be largely personality-agnostic for Moscow, as leadership continues to be shaped by an oligarchy rather than a single individual.

SCENARIO 6: NUCLEAR USE

In early 2025, the Trump administration seeks to end the war in Ukraine through a negotiated settlement. While Ukraine is willing to negotiate, the Kremlin refuses to compromise on its maximalist demands. Following a year of deadlock, during which Russia gradually gains ground, the United States’ European allies provide Ukraine with a large number of long-range missiles in an effort to compel Putin to compromise. Despite the Kremlin’s threats to escalate, Ukraine uses the missiles to strike military and dual-use targets in western Russia. Two weeks into Ukraine’s missile campaign, in early 2026, a Taurus strike kills Chief of the Russian General Staff Valery Gerasimov at a command post in southwestern Russia. Twenty-four hours later, without warning, Russia detonates a sub-kiloton-yield nuclear weapon over a command post in central Ukraine. Putin declares that support for Ukraine has brought the West to “the precipice of Armageddon.” The strike inflicts limited civilian casualties. The United States, the United Kingdom, and France launch a conventional strike of limited effectiveness against the Russian military unit responsible, which is stationed in western Russia. Putin does not retaliate, and the war in Ukraine drags on with continued U.S. aid and restrictions on Ukraine’s use of Western missiles. The international community initially presents a united front in condemning Russia’s nuclear strike, with India discontinuing its purchases of Russian gas and China cutting off support for Russia’s defense industry. A year after the detonation, however, international outrage begins to fade. Many developing states, particularly in Africa and the Middle East, normalize relations with Russia, and China quietly resumes its support for Russia’s defense industry. Three years after the detonation, the war in Ukraine has ended, and—apart from the United States and its allies—most states have resumed normal relations with Russia.

Strategic Objectives: Nuclear use ultimately brought Russia military victory with only short-term political and economic costs; therefore, Russia’s objectives would include solidifying its gains in Ukraine, rebuilding economically, and potentially continuing to expand in the region, backed by nuclear threats that have now proven credible. For the United States and its European allies, the strategic objective will be deterring further Russian aggression and nuclear use in the Euro-Atlantic region. This will require building up both conventional and nuclear capabilities, along with strengthening the credibility of NATO’s deterrent.

Incentives and Opportunities for Arms Control: Prospects for arms control in this scenario would be mixed and largely dependent on the international response. On the one hand, breaking the nuclear taboo after 80 years of non-use, along with the subsequent humanitarian and environmental consequences, should provide an opportunity to highlight the dangers of nuclear weapons and rally international support for new arms control initiatives, as occurred following the Cuban Missile Crisis. On the other hand, the lack of sustained international outrage and Russia’s justification that nuclear weapons use against a military target—when the “existence of the state” was perceived to be at risk—is permissible under international law could signal a normalization of nuclear threats and small-scale use. In this scenario, the broader international response could play a decisive role in prospects for arms control and preventing further nuclear use.

Heather Williams is the director of the Project on Nuclear Issues and a senior fellow in the Defense and Security Department at the Center for Strategic and International Studies (CSIS). She is a member of the Defense Science Board, an associate fellow with the Project on Managing the Atom in the Belfer Center for Science and International Affairs at the Harvard Kennedy School, and a senior associate with the Royal United Services Institute in London.

Nicholas Smith Adamopoulos is an associate director and associate fellow with the Project on Nuclear Issues in the Defense and Security Department at CSIS. His research focuses on alliance dynamics, arms control, and escalation management.

Lachlan MacKenzie is a research associate with the Project on Nuclear Issues in the Defense and Security Department at CSIS.

Catherine Murphy is a program coordinator and research assistant with the Project on Nuclear Issues in the Defense and Security Department at CSIS.