The United States was not the only leading power on the world stage after the end of World War II; it had a new competitor for this power in the Soviet Union. Tensions between the former allies quickly grew, leading to a new kind of conflict—one heightened with the threat of atomic weapons—that came to dominate global politics for the remainder of the twentieth century.

As fighting came to an end in 1945, people the world over faced for the first time the unprecedented extent of destruction and loss of life caused by World War II. As the costs of victory came into devastating focus, the diplomatic responses, rising global tensions between the United States and the Soviet Union, and social disruption that followed in the aftermath of this conflict showed that World War II was truly "the war that changed the world."