How do external security threats affect European integration? This paper examines the impact of the Russo-Ukrainian war on the European Union’s (EU) internal cohesion and governance in boundary changes. Building on the competence-control (CC) framework, we argue that this perceived attack to the EU’s interests triggers policy shifts across security, migration, and sanctions enforcement, reshaping the balance between intergovernmental cooperation and supranational authority. We expect that the war intensified external governance mechanisms and reliance on member-state cooperation but simultaneously empowered the European Commission in agenda-setting and enforcement roles.
To test these claims, we employ a comparative process tracing design that examines causal mechanisms behind the EU's response to the crisis. Preliminary findings reveal a dual outcome: while the EU achieved “community demarcation”—evidenced by unprecedented sanctions coordination and military support—resource disparities and political asymmetries persist, particularly between "inner" and "outer" member states. This research contributes to debates on crisis-driven integration by illustrating how external shocks simultaneously expose weaknesses and create opportunities for institutional empowerment within the EU.