The EU is developing new structures for its Security and Defense Policy and tries to achieve a more integrated security and defense policy. Currently, the principle of unanimity controls the conduct of the EU’s Common Security and Defense Policy. This is one main reason why the EU is in some cases unable to speak with one voice. In the U.S., the President and Congress are the main players in the area of war powers. The President is the most important actor in the area of foreign affairs. However, Congress has the power of the purse and the power to declare war. The role of the courts is rather limited. A good understanding of the respective legal structures of the EU and the U.S. helps the reader to analyze why the U.S. acts in a certain way and why the E.U. may have difficulty to develop a response to a crisis.