For decades, enlargement was one of Europe’s most successful political projects. It extended a community of democracy, prosperity, and stability across a continent emerging from division and conflict. It also unfolded in a strategic environment in which the fundamental questions of European security appeared largely settled.

That assumption no longer holds. Russia’s full-scale invasion of Ukraine has shattered the foundations of the post-Cold War European security order. At the same time, uncertainty about the future of the transatlantic relationship has revived questions about Europe’s own role in defence and deterrence.

The result is that Europe again finds itself facing the relationship between integration and security. And as the first candidate country pursuing accession while fighting a major war on European soil, Ukraine is a special case which occupies a central place in debates about the continent’s future security.

This gives particular significance to proposals such as Chancellor Friedrich Merz’s call for earlier participation in EU institutions and ideas allowing candidate countries progressively to access elements of the Single Market before full membership. Such measures acknowledge that countries undertaking difficult reforms should experience some of the benefits of integration before accession is complete.

Yet in Ukraine’s case, the critical question is no longer how to accelerate accession; it is whether integration into Europe can be discussed separately from the question of European security. The need for credible security guarantees for Ukraine has been recognised since the early stages of Russia’s full-scale invasion. What is changing is the growing realisation that Ukraine’s security and Ukraine’s European integration are becoming part of the same strategic equation.

While NATO membership remains Ukraine’s strategic objective, it is not currently on the horizon. This has increased the urgency of exploring how Ukraine can be anchored within a broader European security framework. Any durable settlement will require more than a ceasefire; it will require a framework that combines political integration, economic opportunity, and credible security guarantees.

The implications are already visible. European defence chief Andrius Kubilius has argued that Ukraine should become part of Europe’s emerging defence architecture. Italian Defence Minister Guido Crosetto has similarly advocated a broader European defence framework extending beyond the EU itself.

Whatever institutional form such arrangements may eventually take, they reflect a broader reality: security is returning to the heart of the European project. Ukraine’s place in this discussion should not be viewed solely through the prism of guarantees and assistance.

After more than four years of war, and with sustained military, financial, and political support from Europe, the United States, and other partners, Ukraine has developed military capabilities and operational experience that few countries in Europe can match. It has also become a source of innovation in areas ranging from drone warfare to battlefield adaptation.

Ukraine isn’t just a recipient of security – it has become a contributor to it.

This reality casts the enlargement debate in a new light. Ukraine’s accession is often discussed in terms of what Europe can offer Ukraine. Increasingly, the question is what Ukraine brings to Europe: military experience, technological innovation, strategic depth, and a demonstrated commitment to defending the principles upon which the European project itself was built.

Ukraine’s successful integration would represent one of the most consequential geopolitical achievements in the history of the Union, not only because it would secure the future of a country under attack but because it would demonstrate Europe’s capacity to adapt its institutions and policies to a profoundly changed strategic environment.

So the debate is no longer simply about enlargement: it is about how Europe responds to the return of hard security questions to the continent and whether it can develop a framework in which political integration, economic integration, democratic resilience, and security cooperation reinforce one another.

One of the enduring lessons of European integration is that lasting security rests not only on military capabilities and deterrence but also on strong democratic institutions, the rule of law, and resilient societies. Ukraine’s future in Europe ultimately concerns all of these dimensions.