["JCMS: Journal of Common Market Studies, EarlyView. ", "\nABSTRACT\nThe European Union's (EU) transformation from a peace project to an assertive geopolitical actor reflects enduring tensions in integration theory dating back to the inter‐war period. This paper develops a comparative framework distinguishing territorial integration logic, which emphasises bounded political communities and collective defence, from cooperative integration logic, which prioritises issue‐specific, transnational problem‐solving. It traces the EU's strategic shift from the cooperative ethos of the 2003 European Security Strategy towards the territorially oriented integration principle represented by the 2016 Global Strategy and subsequent defence initiatives, including Permanent Structured Cooperation (PESCO) and the Strategic Compass. It then revisits inter‐war debates, focusing on Richard Coudenhove‐Kalergi's Pan‐Europe vision, Aristide Briand's United States of Europe proposal and David Mitrany's functionalist critique. Through a systematic comparison of threat perceptions – Russian expansionism, American economic competition and the declining influence of individual European states – and integration responses across both eras, the analysis points to a recurring pattern whereby external crises activate territorial integration impulses."]