World War II (WWII or WW2), also called the Second World War and, in the Soviet Union, the Great Patriotic War, and in Japan, the Second Sino-Japanese War, was a global war involving fighting in most of the world and most countries. Most countries fought in the years 1939–1945 but some started fighting in 1937. Most of the world's countries, including all the great powers, fought as part of two military alliances: the Allies and the Axis Powers. World War II was the largest and deadliest conflict in all of history. It involved more countries, cost more money, involved more people, and killed more people than any other war in history. Between 50 to 85 million people died. The majority were civilians. It included massacres, the deliberate genocide of the Holocaust, strategic bombing, starvation, disease, and the only use of nuclear weapons against civilians in history.
The Japanese victories were stopped in 1942, and the European Axis victories were also stopped by 1943, both in North Africa and in the Soviet Union. After that, the Allies started to fight back from all sides. The Axis lost North Africa and, starting in 1943, were forced to defend Italy. In 1944, the Allies invaded France, heading towards Germany on the Rhine River, while the Soviets kept closing in from the East. Germany surrendered in May 1945. Japan formally surrendered on September 2, 1945. The war ended with the Allied victory.
After the war, the United Nations was set up to develop support between countries and to prevent future wars. The Cold War among the major winners soon started, but they did not fight each other in an actual war. Decolonization of Asia and Africa, where those countries controlled by European countries were given their independence, happened as well. This was because European power was weakened from the war. Economic recovery and the political integration (the process of uniting countries) were among other results of the war.