Luxembourg: Enlargement security moves to the centre of EU diplomacy on Monday 12 October 2026, when foreign ministers meet under the chairmanship of High Representative Kaja Kallas. The agenda lists the security impact of enlargement as a dedicated item, alongside Russia’s war against Ukraine, the Middle East and the situation in Georgia. Ministers will discuss how new members would affect the Union’s security and defence, and how to deepen cooperation with candidate countries now.

The wording of the agenda is revealing. Ministers will consider closer cooperation with candidate and potential candidate countries on the Common Foreign and Security Policy and the Common Security and Defence Policy. That points to a middle path in which candidates take part in security work before they hold a seat at the table, and it makes enlargement security a practical question rather than a slogan.

The timing follows a series of meetings that framed the issue. Defence ministers met in the Foreign Affairs Council format on 28 September, and the EU-Moldova Association Council gathered in Brussels on 5 October, where Kallas said that Transnistria will not block Moldova’s path. The Commission is due to publish its enlargement package on 28 October, so ministers can shape the language before the annual assessments arrive.

Ukraine’s Foreign Minister Andrii Sybiha will join for an informal exchange, a sign that enlargement security is inseparable from the war. Ministers will also review the EU’s response to what the agenda calls intensified Russian hybrid actions, and they are invited to a breakfast on countering foreign information manipulation and interference. Candidate countries sit on the front line of such campaigns, which strengthens the case for sharing intelligence and tools earlier.

My assessment is that enlargement security cuts both ways. A larger Union gains territory, defence industry and experienced armed forces, but it also inherits frozen conflicts, contested borders and exposed energy and information systems. Moldova’s Transnistria region and the unresolved questions in the Western Balkans show that candidates can import risks as well as strengths. Honest debate on that balance is more useful than a list of benefits.

Several practical choices follow. Ministers could invite candidates to more CSDP missions, widen access to European defence procurement, or give them observer roles in selected working groups. Each option raises questions about decision-making, since unanimity in foreign policy already slows the Union of 27. Adding members without reforming voting would make enlargement security harder to deliver, and capitals are aware of that trade-off.

The Luxembourg meeting is unlikely to end with a binding decision, because it is a discussion item. Even so, the conclusions Kallas draws at her press conference will signal how far member states accept security cooperation as a bridge to membership. If they do, enlargement security will become the organising logic of the accession debate heading into the Commission’s package at the end of October.