The start of World War 2 is thought to have been 1st September 1939 with the German invasion of Poland and subsequent declarations of war on Nazi Germany by the British Commonwealth and France. However, many belligerents entered the war before or after this date, during a period which spanned from 1937 to 1941, as a result of other events. Amongst these main events are the Marco Polo Bridge Incident (fought between Nationalist China and Japan), the start of Operation Barbarossa (the Nazi invasion of Russia), and the attacks on Pearl Harbor and British and Dutch colonies in South East Asia.

The end of the War also has several dates. Some sources end it from the armistice of August 14, 1945, rather than the formal surrender of Japan (September 2, 1945); in some European histories, it ended on V-E Day (May 8, 1945). The Treaty of Peace with Japan was not signed until 1951.