EU’s Security Transformation

Europe is experiencing a transformation in its security. At the core of the change is a commitment across the continent to engage in a substantial military rearmament, reversing the trends that saw defense spending decline in the decades after the end of the Cold War. While all of Europe may struggle to reach the 5 percent of GDP in defense spending that was agreed at the NATO Hague Summit in June 2025, significant financing will flow into Europe’s hollowed-out armed forces in the years ahead.

Underpinning the shift is the heightened sense of insecurity and threat that pervades European assessments of the international environment. In the foreground is the direct threat posed by Russia and its war against Ukraine as well as Moscow’s wider efforts to destabilize and challenge the European security order. Behind Russia is a loose coalition of other states—China, Iran, North Korea—which pose various global and regional security and economic challenges and are increasingly working as partners in bilateral, mini-lateral, and, increasingly, larger formats, notably the BRICS, that bring together other key middle powers such as Turkey, India, and Brazil.

But in terms of moving the dial on European defense, the impact of US President Donald Trump cannot be underestimated. It has been the cajoling by the new US administration that Europe must end its free-riding on US security and the real fear in Europe that Trump could abandon the continent’s defense that has finally seen European leaders open the spending taps. The far-reaching changes affecting European security are not, though, simply about funding. As European countries move toward rebuilding their armed forces and looking to a future in which the United States will be a less engaged political and security actor, the key issue of how European security will be managed has emerged.

The Limits of Europe’s Existing Security Architecture

Europe’s current security architecture is not well calibrated for the new international environment that is affecting the continent. For NATO, this is most clearly seen when it comes to Ukraine. Ever since former US President George W. Bush demurred from confronting Russia militarily over its war with Georgia in 2008, Moscow has concluded that the United States is not willing to provide security guarantees to countries outside NATO’s current membership, notwithstanding the “open door” policy remaining in place for Ukraine and Georgia.

Subsequent US presidents have only reinforced doubts about Washington’s commitment as first Barack Obama announced the “US pivot to Asia” and then Joe Biden continually ruled out Ukrainian NATO membership following Moscow’s 2022 full-scale invasion, reflecting the US priorities to avoid war with Russia and to focus on China. Donald Trump has confirmed the established US position limiting its European security commitments by indicating that he will not support Ukraine’s NATO membership. In fact, he is ready for a deal with Russia that would leave Kyiv permanently outside the alliance. This might become obvious as soon as the upcoming Alaska summit meeting between Trump and Russian President Vladimir Putin on August 15.

While the Europeans remain focused on keeping the US in NATO, as seen at The Hague summit, Washington’s European security interests are now providing a clear check on the geographic reach and future scope of the alliance. The US assessment that its national interests do not lie in extending its security guarantees eastward crucially limits the utility of NATO as a vehicle for developing and managing deterrence against Russia and addressing the security challenges of the countries caught between Russia and the Euro-Atlantic community, primarily Ukraine.

Neither is the European Union faring well when it comes to security. Growing internal political divergences have made reaching consensus on sanctions against Russia a painful and protracted process. Meanwhile, Hungary continues to stymie various positions, notably regarding support for Ukraine. The exclusion of the EU from negotiations over the end of the Ukraine war have starkly highlighted the bloc’s weakness. Meanwhile, disunity over Israel’s Gaza war has compounded the sense that the EU is failing as a geopolitical actor. Member states now appear increasingly ready to operate in consensus minus one (or two) formats, to accept the idea of different speeds for the Union, and to re-nationalize policy areas where consensus cannot be achieved.

The central challenge for the EU will be enlargement. Like NATO, the EU retains an open door to Ukraine and has launched the process of membership negotiations. Realistically, this is seen as taking decades with numerous potential hurdles to be overcome inside the EU, in Ukraine, and in the bilateral relationship. Crucially, the key question of how security for new members will be guaranteed is unanswered.

To date, NATO membership has preceded EU membership, but with the US no longer willing to countenance NATO eastern enlargement and Russia ready to use coercion, prospective EU members will be unprotected. Worse, existing EU member states (many of whom are also NATO members) may be on the hook for an unclear, and likely undeliverable, security guarantee to new eastern members through article 42.7 of the Treaty of the European Union. This will create a dangerous confusion about the extent of European security guarantees.

Faced with the complexity of building consensus amongst a politically fragmented Europe and without US leadership, the EU and NATO will struggle to build a strategic approach capable of uniting their respective communities. The longer the vacuum of leadership left by US pullback continues, the more the risks of paralysis and even fragmentation will increase within Europe’s leading multilateral organizations.

The Motor of European Security is European Capitals

While NATO and the EU are receiving most attention regarding the future of European security, the actual drivers shaping the emerging agenda are the European capitals. Crucially, although the EU is positioning itself as a hub for the consolidation of the European defense industry, European rearmament is being led and conducted at the country level. EU member states have been clear that defense remains their competence, and the European Commission is to act as a tool to strengthen national militaries. This has been acknowledged in the ReArm Europe/Readiness 2030 initiative, where the role of the European Commission is to facilitate member state plans with additional funding for their rearmament plans.

Germany stands at the center of security developments on the continent with its huge defense spending plans. The new German government has been clear in its ambition that the country will have the strongest national armed forces in Europe, although it will also continue to work cooperatively with its partners through NATO, the EU, but also via bilateral and mini-lateral agreements and arrangements. Germany’s national focus simply reflects what is happening across Europe, where the dominant pattern is countries conducting rearmament in response to threat perceptions, working closely with trusted partners (often neighbors) that share similar perspectives on security issues.

The Spaghetti Architecture of European Security

With awareness of the limitations of Europe’s existing security architecture growing, countries are increasingly looking to a complex set of interlinked and overlapping ad hoc and sub-regional arrangements as forums for security policy. European leaders are now regularly gathering in a dizzying variety of configurations—the E3 (on Iran), the E4, the E5, the Nordic-Baltic Eight (NB8) and various other configurations including the NB8++, the Joint Expeditionary Force, the Weimar Triangle (and increasingly the Weimar Plus), alongside a plethora of other mini-lateral formats. While many of these formats have been in existence for several years or even decades, they are acquiring a new significance as European countries seek to build effective responses to the security challenges they are facing.

Confronted with limits on NATO’s role in supporting Ukraine, France and the United Kingdom have established the “coalition of the willing” ad hoc mechanism to provide leadership on how European and other supporters of Ukraine can approach the conflict. At the July 2025 UK-France summit, it was even agreed to establish a formal HQ for the group in Paris. This grouping—nominally representing “Europe”—is being used to issue ad-hoc statements about Ukraine and to coordinate and articulate a common European position on US-Russia negotiations to end the war.

The summer of 2025 has seen the consolidation of an informal security triangle composed of Europe’s big three—Germany, France, and the United Kingdom. The UK-Germany treaty of July 2025 and the Franco-UK leaders’ statementfrom the same month, building on the foundational Lancaster House Treaties of 2010, complement the existing Franco-German Aachen Treaty of 2019, creating mutual security assistance commitments and closer defense collaboration between the major European powers as a core element in Europe’s evolving security order.

The importance of working with countries that are considered close and trusted, and likely share similar threat perceptions and therefore capabilities, is underlined by the emergence of states grouping together to make arms purchases, notably between Europe’s small and medium-sized states. The Nordic region is particularly driving these developments, bringing together the region’s defense industry and the acquisition of new weapons systems and common standards, and given shared leadership through the Nordic Defence Cooperation (Nordefco), which has acquired new significance since Sweden and Finland joined NATO. But other groupings are also operating—amongst the Benelux countries, the Baltic states, in Central and Eastern Europe, and across southern Europe, reflecting the imperative at a time of uncertainty to hedge and bandwagon in security ties.

Ordering Europe’s New Security

With Washington’s leadership role fast evaporating, Europe’s coherence as a security community is in doubt. Within this context, the ad hoc and informal formats have gained a new prominence as a means to build European leadership and to generate quick action when NATO and the EU cannot deliver. But with the United States now apparently set on shifting away from Europe, there is a clear risk that the established European security order could atrophy in the absence of Washington’s engagement.

Europe’s security transformation is, thus, not just about money and capabilities, it is about leadership. To ensure that the security transformation does not produce a diminished Europe, capitals must begin to assert a new vision for how the continent’s security governance should be structured and led. For while the EU and NATO will doubtless persist, with a reduced US leadership their value will likely be as instruments to implement policy that will be politically agreed in informal and sub-regional formats.

European countries must therefore begin to look at their ad hoc security architecture not as a temporary fix to bridge current uncertainties or even as a threat to existing organizations but rather as a key element of an emergent new security order and, crucially, as a means to generate European leadership. As the recent convening of the ad hoc group of European leaders ahead of the US-Russia summit has demonstrated, this type of format is attractive because it can deliver fast and effective action, trumping Europe’s traditional focus on integration and consensus.

But this approach also brings risks. At present, efforts to assert European leadership are emerging reactively and in response to crises. Such formats, by definition, are not inclusive, with membership defined by those who are “likeminded” or who bring significant resources to the table. An unthought-through embrace of functional and regional formats risks creating an uncoordinated approach and further fragmentation.

As Europe moves away from a security order that has been defined, to a large degree, by US power and strategic vision, there is, thus, a need to shape a new political architecture to fit with the new European security. To assert their leadership effectively, European leaders should work to develop one of the key ad hoc political formats—“the coalition of the willing” and the Weimar Plus grouping are currently the leading contenders—as a forum for developing strategic leadership on European security policy.

Such a body should aim to coordinate the initiatives on security and defense that are taking place within Europe’s existing multilateral institutions and the growing set of informal groupings to support that vision and, in this way, ensure a continued coherence for a European security community. This is now an urgent challenge, since Europe’s future security will depend not only on producing enough aircraft and tanks, but on having the ability to develop and implement together defense and deterrence.

Neil Melvin is Director, International Security at the Royal United Services Institute (RUSI) in London.