As the war drew to a close, the nations of the world were eager to find a means of attaining permanent peace. In 1945, the United Nations was established and its charter was signed by 51 countries. However, threats to the friendly settlement of postwar problems appeared even before the charter was signed. The Soviet Union, for example, had antagonized the United States and Great Britain by annexing the Baltic states (Estonia, Latvia, and Lithuania) and by making extreme reparations demands upon Germany, Hungary, and Poland.

After the war, the Soviets disagreed with the other Allies about the application of the agreements they had reached concerning the status of conquered and occupied territories. Although they had promised to allow self-determination for the people of the territories they had occupied, the Soviets brought most of the Balkan nations under Communist rule. They also supported rebels in Greece, Turkey, and Iran, aided the Communist uprising in China, and closed off eastern Europe—including the Soviet occupation zone of Germany—to the outside world. These actions led to a prolonged period of tension called the "cold war" between the Western powers and the Soviet Union. Soviet-dominated Europe, said Winston Churchill, was separated from the rest of the world by an "iron curtain."