After the longest dry spell in its enlargement history, the European Union is moving again. On October 6, the European Commission presented its communication “Preparing for a Wider Union,” concluding that the EU can accommodate a larger membership if it adapts its policies and decision-making. “These changes need to make sure that a larger European Union is also a stronger Union,” Enlargement Commissioner Marta Kos said.
Indicative roadmaps for Montenegro, Albania, Moldova, and Ukraine are due with the enlargement package at the end of October, and EU leaders take up the debate at the European Council on October 15–16.
Yet, the real significance of this moment lies beyond the bureaucratic shifts in the process. EU enlargement has become a geopolitical and, above all, a security question. In a changing European security order, it is one of the most powerful instruments the EU has.
Driving the Shift
Two developments are driving this shift. The first is Russian revisionism, with the full-scale war of aggression against Ukraine and Moscow’s continued threats to redraw borders in Europe by force. The second is the upheaval in transatlantic relations. Transatlanticists and skeptics alike increasingly agree that Europeans must take on greater responsibility for their own security, especially since security today is no longer only military: Hybrid attacks, economic coercion, and the use of dependencies in energy and supply chains as pressure points are part of it.
The EU has also learned, painfully, what happens when steps toward integration lack a security dimension. The events in Ukraine in 2013 and 2014 showed that economic and political rapprochement without a credible security perspective quickly reaches its limits; while the Maidan revolution affirmed the country’s Westward orientation, Brussels was unable to deter or counter Russian designs on Ukraine and only made it a candidate country after the full-scale attack eight years later. Security and defense cooperation, therefore, is not a reward for successful integration. It is its precondition.
Making Security the First Step of Gradual Integration
Something fundamental changed earlier this year: Germany and France, long the brakemen of EU enlargement, moved to the front and revived an old idea: gradual integration. With its October 6 communication, the European Commission has now made the concept its own. Candidate countries are to take part in selected EU policies before accession, in a way that is “conditional and reversible” and complements rather than replaces membership. Notably, the European Commission names defense among the strategic sectors and calls for “closer security and defense cooperation before accession.”
What is still missing is a starting point—a clear idea of what needs to come first. Without one, gradual integration risks turning into a menu of sectors to choose from, without a sequence. Yet, the basis for an obvious first step already exists. In July, the EU opened Cluster 6 on external relations in the accession negotiations with Ukraine and Moldova, including Chapter 31 on foreign, security, and defense policy. Both countries bring hard-won assets to the table: Ukraine its battlefield experience and the most dynamic defense-industrial ecosystem in the world, Moldova its resilience against hybrid threats.
Implementing the concept of gradual integration in the real world should now mean that closing this cluster triggers the first stage of deepened integration: a pre-accession security agreement tailored to each country’s domestic realities and political room for maneuver. Brussels’ guiding principle should be to offer as much as possible. For future candidate countries, the same logic should apply from the outset: The security chapters should be opened immediately, alongside the fundamentals, rather than leaving them until the end.
Using the Tools Already on the Table
Such agreements need not wait for treaty change. Since 2020, “third states” (i.e., non-EU members) can be invited to join PESCO projects–the treaty-based Permanent Structured Cooperation framework for member states to jointly plan, develop, and invest in collaborative capability development and to enhance the operational readiness of their armed forces. Canada, Norway, the United States, and the United Kingdom already take part in the Military Mobility package that was launched in November 2025. Candidate countries should be next. Article 44 of the Treaty of the European Union (TEU) allows the European Council to entrust missions to groups of willing and able member states, and candidate countries should be able to contribute personnel and equipment to Common Security and Defense Policy (CSDP) missions going forward. Their participation in a future security mission for Ukraine should become a cornerstone of the entire process.
Defense industry cooperation is the second lever. The wars in both Ukraine and Iran show that industrial capacity, endurance, and rapid innovation are themselves a layer of deterrence, one that the Europeans urgently need to build. The European Commission has proposed €131 billion for defense, security, and space in the next long-term budget (covering the years of 2028 to 2034), five times more than in the current budget.
Candidate countries should move from existing arrangements to full participation in the European Defense Agency, gain access to the European Defense Fund, and join the EU’s investment screening framework to keep rival powers away from critical bottlenecks. (China’s export controls on rare earths have shown how quickly supply chains become leverage.) This way, both sides win: Candidate countries gain access to EU structures and funding, member states and the EU as a whole gain capacity and surge potential.
One core question that remains, however, is the one about security guarantees. Article 42.7 TEU, the EU’s “mutual assistance” clause, does not offer a convincing answer. It is operationally vague, qualified by the special character of neutral EU member states’ policies (such as Austria and Ireland), and applies only to existing member states, not candidate countries.
Instead, a “coalition of the willing”-style European Defense Union built on the Schengen model—outside the existing treaties and open to those who choose to join—could provide what the treaties cannot: a mutual commitment made credible precisely because its members opted in. Candidate countries should be offered early participation, as members or close partners. One size will not fit all: Montenegro and Albania are NATO allies, Moldova is constitutionally neutral, and Ukraine is at war. But the Europeans’ ambition and need to take primary responsibility for their own security require new formats and approaches.
Germany’s Role
Germany must lead this process, and not merely because of its weight. The ambition to build “Europe’s strongest conventional army” will strengthen the European project only if it is deeply interwoven with Germany’s partners. Pursued as a national project, it would alarm neighbors and divide allies, undermining the very goal of a safer continent.
Germany’s National Security Strategy promises a European approach; a security and defense-oriented EU enlargement policy is where Berlin can prove it. As has been argued in this series, Germany needs to play a key role in making the EU “enlargement-ready.” But time is short: The far-right Alternative für Deutschland’s (AfD) winning 43.8 percent of the vote in Saxony-Anhalt in September is a reminder that domestic backing for such a course cannot be taken for granted.
EU leaders should therefore send two signals: a clear political commitment to enlargement, and a concrete mandate to make security and defense the priority in the roadmaps due to be published at the end of October. European prosperity rests on a rules-based order that is increasingly under attack; only an integrated continent can defend it. For too long, the EU has treated enlargement as a reward for reform. It must now see it for what it is: security policy.
N.B. The views expressed are solely those of the authors.
Ralf Roloff is a professor at the Bundeswehr University Munich and the deputy dean of academics at the George C. Marshall European Center for Security Studies.
Tom Kühnel is a research assistant at the Bundeswehr University Munich and a Master of International Affairs student at the Hertie School in Berlin.
