The European Council as the Mother of EU Enlargement: navigating widening and deepening beyond the formal Treaty rules

At least since Russia’s invasion of Ukraine in early 2022, the prospect of enlargement of the European Union (EU) is high on the agenda of policymakers and scholars alike. The European Commission has proposed that member states start negotiations with applicant countries, notably with Ukraine. Meanwhile, scholars stress that any further "widening" of the Union should go hand in hand with "deepening", that is EU institutional and policy reforms. This paper analyses how the European Council, the actor in charge of opening and concluding accession negotiations, has addressed EU enlargement over time. Using a novel dataset including all 240 European Council conclusions since 1969, we document how national leaders have framed former and more recent rounds of enlargement. We find that the willingness to enlarge indeed overlaps with concerns about the EU’s internal functioning. In every enlargement round, national leaders established "master narratives", often framing enlargement as a geopolitical necessity for the current member states and a means for democratic consolidation in the applicant countries. Doing so, national leaders go well beyond the mere legal basis, with Article 49 TEU providing vague formulations and only suggesting a secondary role for the European Council in enlargement.