World War II

Canada's foreign policy had changed somewhat during the interwar period. Closer political and economic ties with the United States had resulted in a more North American than European orientation. Isolationism was a growing trend. The outbreak of World War II in 1939, however, embroiled Canada again in European affairs. In addition to supplying war materials, the Canadians soon began to send troops to the battle zones. The Royal Canadian Air Force took part in the Battle of Britain, 1940–41. During the battle's most crucial phase, when it appeared that the Germans might be able to invade England, plans were made to transfer the seat of the Commonwealth to Canada.

Canada, which had declared war on Germany in 1939, followed with declarations of war against Italy in 1940, and against Hungary, Finland, Romania, and Japan in late 1941. In 1942 the manpower demands of the war led the government to send conscripted troops overseas, despite protests by Quebec. Canadian units took part in the invasions of Sicily and the Italian mainland in 1943, the assault on Normandy in 1944, and the conquest of Germany in 1945. By the war's end, Canada had mobilized an armed force of more than one million out of a population of about 11,500,000 (1941 census).