The balance of power from the early 20th century onward underwent drastic changes that for all practical purposes destroyed the European power structure as it had existed since the end of the Middle Ages. Prior to the 20th century, the political world was composed of a number of separate and independent balance-of-power systems, such as the European, the American, the Chinese, and the Indian. But World War I and its attendant political alignments triggered a process that eventually culminated in the integration of most of the world’s nations into a single balance-of-power system. This integration began with the World War I alliance of Britain, France, Russia, and the United States against Germany and Austria-Hungary. The integration continued in World War II, during which the fascist nations of Germany, Japan, and Italy were opposed by a global alliance of the Soviet Union, the United States, Britain, and China. World War II ended with the major weights in the balance of power having shifted from the traditional players in western and central Europe to just two non-European ones: the United States and the Soviet Union. The result was a bipolar balance of power across the northern half of the globe that pitted the free-market democracies of the West against the communist one-party states of eastern Europe. More specifically, the nations of western Europe sided with the United States in the NATO military alliance, while the Soviet Union’s satellite-allies in central and eastern Europe became unified under Soviet leadership in the Warsaw Pact. here