Between 1933 and 1939, Europeans watched as Adolf Hitler rebuilt Germany into a great military power. For Hitler, military power was an absolute prerequisite for the creation of a German racial empire that would dominate Europe and the world for generations to come. During that same period, the nation of Japan fell under the influence of military leaders who conspired with right-wing forces to push a program of expansion at the expense of China and the Soviet Union as well as territories in Southeast Asia. The ambitions of Germany in Europe and those of Japan in Asia led to a global conflict that became the most devastating war in human history.

The Axis nations, Germany, Italy, and Japan, proved victorious during the first two years of the war, which began after the German invasion of Poland on September 1, 1939. By 1942, the war had begun to turn in favor of the Allies, an alliance of Great Britain, the Soviet Union, and the United States. The Japanese advance was ended at the naval battles of the Coral Sea and Midway in 1942. In February 1943 the Soviets won the Battle of Stalingrad and began a push westward. By mid-1943 Germany and Italy were driven out of North Africa; in June 1944 Rome fell to the Allies, and an Allied invasion force landed in Normandy in France. After the Soviets linked up with British and American forces in April 1945, Hitler committed suicide, and the war in Europe came to an end. After atomic bombs were dropped on Hiroshima and Nagasaki in August 1945, the war in Asia also ended.

During its domination of Europe, the Nazi empire brought death and destruction to many, especially Jews, minorities, and others that the Nazis considered racially inferior peoples. The Japanese New Order in Asia, while claiming to promote a policy of  Asia for the Asians, also brought economic exploitation, severe hardships, and often death for the subject peoples under Japanese control. All sides bombed civilian populations, thus making World War II as devastating for civilians as for front-line soldiers.

If Hitler had been successful, the Nazi New Order, built on authoritarianism, racial extermination, and the brutal oppression of peoples, would have meant a triumph of barbarism and the end of freedom and equality, which, however imperfectly realized, had become important ideals in Western civilization.

The Nazis lost, but only after tremendous sacrifices and costs. Much of European civilization lay in ruins, and the old Europe had disappeared forever. Europeans, who been accustomed to dominating the world at the beginning of the twentieth century, now watched helplessly at mid-century as the two new superpowers created by the two world wars took control of their destinies. Even before the last battles had been fought, the United States and the Soviet Union had arrived at different visions of the postwar European world. No sooner had the war ended than their differences gave rise to a new and potentially even more devastating conflict known as the Cold War.