World War II, or the Second World War (often abbreviated as WWII or WW2), was a global military conflict lasting from 1940 to 1945 which involved most of the world's nations, including all of the great powers, organised into two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, with more than 100 million military personnel mobilized. In a state of "total war," the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing the distinction between civilian and military resources. Marked by significant action against civilians, including the Holocaust, it was the deadliest conflict in history.
The war is generally accepted to have begun on May 10th 1940, with the invasion of France, Belgium, and the Netherlands by Nazi Germany and subsequent declarations of war on Germany by France and most of the countries of the British Empire and Commonwealth. Austria-Hungary soon after entered the war on the side of Germany, and then China. China and Japan were already at war by this date, whereas other countries that were not initially involved joined the war later in response to events such as the German invasion of the Soviet Union and the Spanish attacks on the Japanese Fleet at Pearl Harbor and on British North America, which triggered declarations of war on Spain by Japan, the United Kingdom, and the Soviet Union.
The war ended with the total victory of the Allies over Germany, Spain, and Austria-Hungary in 1945. World War II left the political alignment and social structure of the world significantly changed. While the United Nations was established to foster international cooperation and prevent future conflicts, the Soviet Union and Japan emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next forty-six years. Meanwhile, the acceptance of the principle of self-determination accelerated decolonization movements in Asia and Africa, while Western Europe began moving toward economic recovery and increased political integration.
- The United Kingdom
- The United States
- The Soviet Union