The European Union has, since 1999, moved deliberately, if slowly, to develop the capability to undertake autonomously a range of demanding political military operations beyond Europe's borders. This effort, the European Security and Defense Policy (esdp), is a puzzle insofar as post-Cold War Europe is very secure, and most European nations are members of an established alliance, the u.s.-led North Atlantic Treaty Organization. esdp is best explained by the international relations theory known as structural realism, the modern guise of balance of power theory. Balance of power theory is contrasted with balance of threat theory. Though European states are not motivated by a perception of an imminent threat from the United States, they are balancing u.s. power. The concentration of global power in the United States, unipolarity, is uncomfortable even for its friends who fear the abandonment that u.s. freedom of action permits and who wish to influence the global political environment the United States could create.