Italy surrendered to and then joined the Allies in late 1943. Germany surrendered to the Allies in May of 1945, the date of which was officially called V-E Day, for victory in Europe. The war ended on 2 September 1945 with the formal surrender of Japan, called V-J Day, for victory in Japan.

Approximately 62 million people died in the war. Most were civilians, as a result of the large-scale aerial bombing of cities, disease, starvation, and genocide (see the Holocaust). It is guessed that the Soviet Union suffered around 23 million deaths, and that China suffered about 10 million. Poland suffered the most deaths in proportion to its population of any country, losing 5.6 million out of a pre-war population of 34.8 million.

The war was responsible for the re-drawing of national boundaries and the creation of new nations, the end of western colonialism, and the beginning of the Cold War.

After World War II, Europe was informally partitioned into Western and Soviet spheres of influence. Western Europe largely aligned as NATO, and Eastern Europe largely as the Warsaw pact. There was a fundamental shift in power from Western Europe and the British Empire to the new superpowers, the United States and the Soviet Union, with significant boundary changes and displacement of people as the Soviet Union's borders shifted westwards.

In Asia, the United States' military occupation of Japan led to Japan's democratization. China's civil war continued through and after the war, resulting eventually in the establishment of the People's Republic of China. The former colonies of the European powers, such as India, Indonesia, and Vietnam, began their road to independence.

Finally, the war saw a number of newly developed weapons that were used against either military and civilian targets. Atomic weapons, long range missiles, jet aircraft, and radar, are only a few of many wartime inventions that changed the nature of future conflict.