Before this study was conducted, there was a research gap in the current field of international relations. The purpose of this study was to examine why the EU has not established a common defence policy and a common defence. In order to address this, a theoretical framework based on realism and liberalism was created. Taken together, this study thus filled that gap and provided new insight on EU’s defence policy. The method that was used to conduct the research was a case study and the material consisted of the Treaty of Lisbon, EU key documents, as well as numerous of theoretical works concerning realism and liberalism. The study is of an explaining nature and the analysis seeks to explain the research question by testing it on the theoretical framework. The study concludes that the theoretical framework is able to explain the research question. Both realism and liberalism contributed with significant insight on why the EU has not established a common defence policy and a common defence. The main result shows that realism answers the research question by pointing out the role that member states play, and that liberalism, in contrast, points at the role EU as a unitary institution plays.

One of the major analytical shortcomings regularly made by EU and NATO experts today lies with exclusively seeing the European defence project as a post-World War II (WWII) phenomenon and the EU’s Common Security and Defence Policy (CSDP) as mainly a post-Cold War product. No analyst has so far seriously explored the idea of European defence predating WWII and the 20th century. Instead, since 1999 one frequently reads and hears about the ‘anomalous,’ ‘elusive’ CSDP suddenly complicating transatlantic relations. But the CSDP is hardly an oddity or aberration, and it is certainly not as mysterious as some might suggest. Drawing extensively from primary sources and predicated on an overarching evolutionist approach, this thesis shows that the present CSDP is an ephemeral security and defence concept, only the latest of its kind and full of potential. Drawing its deepest ideational roots from the (pre-)Enlightenment era, the CSDP leads to a pan-European defence almost irreversibly. A common defence for Europe is quite possible and, due to the growing impact of the exogenous (multipolar) momentum, can be realized sooner rather than later even without a full-fledged European federation. / May 2016