Post Cold War USEuropean Security and Defense Relations Zhang Yeliang (21) The end of the cold war has posed serious challenges to the traditional USEuropean security and defense relationship based on NATO alliance. With the change of European security environment and the nature of defense, the strategic focus of the United States and Europe has shifted respectively. The nature and content of USEuropean security and defense relations have also changed in accordance to the progress in EU integration and the further strengthening of American power. The Sept. 11 terrorist attack has not reversed the trend of widening split in USEuropean relations. Rather, its aftermath poses yet another serious challenge to USEuropean relations. Although there are numerous differences on the issues of security and defense between the United States and Europe, such rifts will not become adrift. Coordination and cooperation will still be the keynote in the relationship.