World War II, or the Second World War (often abbreviated as WWII or WW2), was a global military conflict lasting from 1939 to 1945, which involved most of the world’s nations, including all of the great powers: eventually forming two opposing military alliances, the Allies and the Axis. It was the most widespread war in history, with more than 100 million military personnel mobilised. 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 events involving the mass death of civilians, including the Holocaust and the only use of nuclear weapons in warfare, it was thedeadliest conflict in human history, resulting in 50 million to over 70 million fatalities.
The war is generally accepted to have begun on 1 September 1939, with the invasionof Poland by Germany and Slovakia, and subsequent declarations of war on Germany by France and most of the countries of the British Empire andCommonwealth. Germany set out to establish a large empire in Europe. From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or subdued much of continental Europe; amid Nazi-Soviet agreements, the nominally neutral Soviet Union fully or partially occupied