Almost immediately following the end of the Second World War, the competing economic and social systems of the United States and its European allies, on the one hand, and the Soviet Union and its allies, on the other, spawned the Cold War. This period of heightened military tension and mutual suspicion lasted more than four decades, as each side struggled to expand its influence — and limit that of its rival — through economic, political, and occasionally military activity. The postwar decades were also times of revolutionary change outside the West. The war weakened the grip of European nations on their overseas colonies, and nationalist movements in Asia, the Middle East, and Africa won independence for former colonies. In many cases, decolonization proceeded relatively peacefully. In others, the struggle for independence produced violent clashes. In all cases, however, the process of decolonization and subsequent efforts at nation building were shaped by the battle between the United States and the Soviet Union for global influence.