Differentiated Integration as a Response to Enlargement Fatigue: Assessing the Balance Between Flexibility and Cohesion in the EU

This paper explores how successive rounds of European Union enlargement have expanded the EU’s geopolitical influence while simultaneously deepening institutional, political, and legal fragmentation. It focuses on differentiated integration as a key mechanism developed to manage this diversity without undermining the Union’s capacity to govern effectively. Drawing on academic literature, legal frameworks, and policy analyses, the study examines how differentiation has been implemented across core areas such as defense, migration, and economic integration. Special attention is given to institutional tools like enhanced cooperation, opt-outs, and association agreements, assessing both their practical consequences and their broader normative implications. By situating these developments within theoretical debates as well as concrete case studies, the paper evaluates the delicate balance between flexibility and unity in the EU. The analysis is particularly timely in light of renewed enlargement momentum, including Ukraine’s candidacy and ongoing debates about internal reform.