Dates when countries entered WW2 By rowennkk Period: Jul 7, 1937 to Sep 9, 1945 Second Sino-Japanese war begins between Japan and China Period: Sep 3, 1939 to Sep 2, 1945 New Zealand, Britain, France, India, Australia and South Africa enter WW2 on the allies Period: Sep 10, 1939 to Sep 2, 1945 Canada enters WW2 on the allies Period: Jun 10, 1940 to Sep 8, 1943 Italy enters WW2 on the Axis Power Period: Jun 22, 1941 to Sep 2, 1945 Soviet Union enters WW2 Period: Dec 8, 1941 to Sep 2, 1945 USA enters WW2 on the allies Period: Oct 13, 1943 to Sep 2, 1945 Italy declares war on Germany, enters Allied side