ESDP-NATO comparison in the establishment of European security according to realist perspective

European states have been seriously damaged due to both civil wars and two great world wars. This is the reason European states needed an integration process after the Second World War due to ensure the damage and protection against threats in the Cold War. In fact, it does not seem possible military and political integration immediately for European states which fighting many years. Therefore, the European states that have entered the process of economic integration had to hand over their security to NATO due to economic inability. During the cold war, NATO was the only organization which responsible for European security. After the Cold War, European Union tried to establish a common security and defence policy due to changing international conditions. NATO was concerned about the EU's attempts to establish a common security policy. Accordingly the relationship between NATO and the European Union has been studied using realism theory which examine international relations through the concepts of power and interest. Our aim in this thesis is to discuss why the EU needs a common security and defence policy. Our aim is to answer the question of whether NATO and the EU are rivals or partners from a realist perspective. Key Words: NATO, European Union, Realism, Cold War, Security