As of 2021, the European Union (EU) is now a foundational part of Europe’s defense architecture, with programmes such as PESCO now enabling the EU to organise civil-military responses to crise and coordinate the defense-planning cycles of 25 European countries. This article asks why EU member states have opted to use the EU to enable their capabilities and manage ongoing security crises? In answering this question, the article uses a pluralistic reading, utilising realist and liberal-intergovernmentalist frameworks to assess complementary hypotheses for this cooperation. The second part assesses the state of the international system, concluding its increasing insecurity has prompted a collective awareness that a more strategic response to collective security is necessary. The third part evaluates the role of the political and economic balance of bargaining power between EU member states, assessing Germany, France, and Poland as case studies. The paper concludes briefly on the implications of this cooperation and the need for pluralistic readings of EU defense cooperation.