The author analyzes the role the U.S. Supreme Court envisions for different branches in the area of foreign relations law. An in-depth analysis of its case law leads to the conclusion that the Court has de facto played an important role in the growth of presidential power. The current situation in the area of war powers and regarding the treaty power seems to pose a major threat to the system of checks and balances of the U.S. Constitution. The author examines if a new approach could avert the inherent danger of executive unilateralism. Such an approach could be inspired by the Constitutional Court in Karlsruhe. Since the 1990ies the German Justices try to bolster the role of the Federal Diet in questions regarding the use of armed forces abroad and the process of European integration.