The EU's emergence as an international security actor is one of the most striking developments in the history of European integration. After decades of debate about the need for a Common Security and Defence Policy (CSDP), the EU has developed a European Security Strategy and launched over twenty foreign CSDP security missions since 2003. These initiatives, in turn, have inspired several theoretical explanations of the CSDP phenomenon, many of which are related to realism (i.e., balance-of-power and balance-against-threat theories). However, the empirical record of actual CSDP operations does not support such explanations.
Instead, this paper offers an explanation of the EU's new security 'actorness' based on the concept of experiential institutional learning. Specifically, I argue that EU treaties are limited in describing CSDP functionality, so the EU has had to engage in a high degree of institutional improvisation in this area. This improvisation has inspired new institutional roles and capacities, and it suggests a capacity for endogenous institutional development on the part of the EU. Next, I argue that the EU's CSDP operations represent a type of EU capacity-building intended for the purpose of providing the EU with operational experience in order to enhance its reputation and effectiveness as a global security actor. This capacity-building often takes the form of 'experiential institutional learning', defined as a change in an institutions responsibilities, rules, and resources as a result of new information, observation, or experience. Finally, I demonstrate the extent to which such learning is taking place in the development of the CSDP capacity by examining the full range of CSDP operations undertaken between 2003 and 2011.
