Montenegro leads EU enlargement queue as bloc debates new accession model

For the first time since Romania and Bulgaria signed their accession treaties in 2005, the European Union has convened a working group to draft a treaty for a new member. The candidate is Montenegro, a country of roughly 620,000 people, and the move marks the most concrete step towards enlargement in nearly two decades. Enlargement Commissioner Marta Kos presented the working group as evidence that the EU is finally matching words with action. "Enlargement is the priority for the European Union, and if our candidates deliver, then we have to deliver, too," she told foreign ministers meeting in Brussels in early May.

Montenegro leads the queue as enlargement returns to centre stage

The symbolism is deliberate. After years of stalled negotiations with Turkey, frozen talks with North Macedonia and Albania, and a western Balkans process that seemed designed to manage expectations rather than fulfil them, Brussels needed a visible milestone. Montenegro, having closed all negotiating chapters in December 2024, offered the path of least resistance. Analysts agree it is the only candidate with a realistic timetable. "There is no clearer signal that the EU sees Montenegro as its next member state," said Strahinja Subotic of the European Policy Centre in Belgrade.

Yet the working group also exposes how far the EU has drifted from the enlargement momentum of the early 2000s. The last major wave brought in ten countries in 2004, followed by two more in 2007 and Croatia in 2013. Since then, the process has been bogged down by rule-of-law disputes, bilateral vetoes, and a growing conviction among several capitals that the Union must reform before it expands. The result is a paradox: enlargement is officially a geopolitical imperative, yet the machinery to deliver it remains half-built.

The geopolitical shift after Ukraine invasion

Russia's full-scale invasion of Ukraine in February 2022 forced a strategic rethink. What had been treated as a technical, merit-based process became a security question overnight. Ukraine, Moldova and Georgia were granted candidate status in record time. The western Balkans, long stuck in a waiting room, were told their integration was now a matter of European defence. "The geopolitical need for enlargement is recognised by all member states," said Steven Blockmans of the Centre for European Policy Studies in Brussels. "But it is always coupled with two things: on the one hand, a merits-based approach, whereby candidate countries are assessed on their reforms and where no shortcuts are being offered, and secondly, the need for the European Union to change its policy and governance methods."

That second condition, institutional reform, is where consensus fractures. The EU still operates largely on a methodology designed for the 1980s and 1990s, when candidates were smaller, economically closer to the EU average, and the Union itself had fewer competences. Today's candidates include Ukraine, a country of 37 million at war, and a western Balkans region where state capture and media freedom remain serious concerns. Commissioner Kos acknowledged the mismatch: "What we are now discussing with the member states is whether gradual integration principles, which we are mainly using in the single market, could also be moved to other areas, especially security."

Merz's proposals and the staged accession debate

Into this vacuum stepped Friedrich Merz, elected German chancellor in early 2025. In a recent enlargement proposal, he called for all negotiation clusters with Ukraine to be opened immediately and floated a form of "associate membership" that would embed Kyiv in EU institutions and foreign policy coordination before full accession. For the western Balkans and Moldova, he suggested privileged single market access, observer status in EU bodies, and gradual integration into decision-making. The ideas are not new. Blockmans, one of the architects of the "staged accession" model, noted that elements have already entered mainstream thinking through the EU's Growth Plan for the western Balkans and proposals from France, Germany and Lithuania. "You see elements of a more staged approach, whereby benefits for reforms are being offered in earlier pre-accession phases of the process," he said.

The logic is straightforward: reward reform with tangible integration, market access, programme participation, institutional presence, rather than keeping everything locked behind the final treaty. The Growth Plan for the western Balkans, adopted in 2023, already offers €6 billion in grants and loans conditional on reform milestones, with the explicit aim of bringing the region closer to the single market before membership. But the model's limits were tested quickly. The idea of "reverse enlargement", admitting Ukraine formally and completing reforms afterwards, backed by President Volodymyr Zelenskyy and parts of the Commission, was rejected by member states almost as soon as it surfaced. The merit-based principle, it turned out, still has teeth.

The veto rights controversy

More contentious still is the question of decision-making power. In an enlarged EU of 30 or more members, unanimity requirements in foreign policy, taxation and parts of justice and home affairs look increasingly unworkable. One proposal, developed within the staged accession framework by Blockmans and Subotic, suggests temporarily limiting veto rights for new members after accession. The goal, Subotic insisted, is not to create "second-class membership" but to reassure sceptical capitals that enlargement will not paralyse the Union. "It could apply only to one or two policy areas and not necessarily in the same way or for the same duration for every candidate country," he said.

Legally, such a mechanism could be written into accession treaties. Politically, it touches the raw nerve of sovereign equality. The treaties enshrine the principle that all member states are equal in rights and obligations. Carving out exceptions, even temporary ones, would require unanimity among existing members, the very veto the reform seeks to constrain. Several western Balkans governments have signalled pragmatism. Albania, Bosnia and Herzegovina and Serbia have all indicated they would accept temporary limitations if that unblocked their path. Montenegro, however, has refused. Having negotiated under the current rules, Podgorica sees no reason to accept a diluted status at the finish line.

Western Balkan positions diverge

The split reveals different calculations. For Serbia and Bosnia, where EU enthusiasm is cooler and domestic politics more volatile, a faster track with conditions may be the only politically saleable option. Albania, further advanced in negotiations, may calculate that transitional restrictions are a price worth paying for certainty. Montenegro's stance is simpler: it has done the work, closed the chapters, and expects the contract on the terms agreed. Analysts believe it will be the last country to join under the unreformed system. "It is likely to be the last country to enter the EU under the bloc's current rules before any deeper institutional reform takes place," one researcher noted.

That makes Montenegro's treaty a test case. Subotic expects the accession agreement to include stronger post-accession monitoring tools than previous rounds, particularly on rule of law and democratic backsliding, a direct response to the Hungarian and Polish experiences where Article 7 procedures proved toothless. "One might expect Montenegro to become the guinea pig to explore the limits of transitional arrangements and safeguard clauses," said Blockmans. The treaty currently being drafted could become the template for Ukraine, Moldova and any future candidates.

Montenegro as template for future accessions

The implications stretch beyond Podgorica. If the EU can design a treaty that embeds enforceable safeguards, phased integration, and perhaps even conditional voting rights, it creates a model flexible enough for a war-torn country of 37 million and a microstate of 600,000 alike. But the political will to codify such innovations remains untested. The working group drafting Montenegro's treaty operates under the current legal framework. Any departure, veto limitations, enhanced monitoring, staged rights, requires agreement among the 27. That means the same capitals that have blocked reform for years must now approve it in a treaty text.

Commissioner Kos has framed the working group as a delivery on the EU's promise. The harder question is whether the promise itself is being rewritten. The staged accession model, the Growth Plan, the associate membership concept, all are attempts to square a circle: how to enlarge without reforming the institutions that make enlargement work. Montenegro's treaty will show whether the EU has found an answer or merely bought time.