On September 9, 1939, eight days after Germany’s invasion of Poland, Canada’s Parliament voted to declare war on Germany, which the country did the next day. (Its separate declaration of war was a measure of the independence granted it in the 1931 Statute of Westminster; in 1914 there had been no such independence and no separate declaration of war.) The vote was nearly unanimous, a result that rested on the assumption that there was to be a “limited liability” war effort that would consist primarily of supplying raw materials, foodstuffs, and munitions and the training of Commonwealth air crews, mainly for the Royal Air Force. Canadian men were to be actively discouraged from serving in the infantry, which was expected to take high casualties, and it was anticipated that few infantry units would be formed. If this plan were followed, King and other government leaders reasoned, conscription would be unnecessary. King and the leader of the Conservative opposition had both pledged themselves to a “no conscription” policy even before the war began.

The expulsion of the British from the Continent and the fall of France in the spring of 1940 totally changed the circumstances. Canada’s overseas allies had fallen or were in danger of doing so, and the country immediately concluded an agreement at Ogdensburg, New York, with the United States for the defense of North America. Moreover, Canada now stood in the forefront of the war. After Britain, it was (prior to the U.S. entry into the war in December 1941) the second most powerful of Germany’s adversaries. The emphasis on supply gave way to a focus on combat forces. King’s “no conscription” policy had been modified in 1940 when the government introduced conscription for home defense, but at the same time King renewed his pledge not to send conscripts overseas for “active” duty. In 1942 the King government called a national plebiscite asking Canadian voters to release it from that pledge; nearly two-thirds of Canadian voters supported conscription, though in Quebec three-fourths opposed it. Thereafter the government enforced compulsory service for home defense, but King, fearing an Anglo-French cleavage, did not send conscripts overseas during the early years of the war, preferring to avoid such a move unless absolutely necessary.

Still, Canadians were deeply enmeshed in the war. Under increased pressure from military leaders to move Canadian troops into battle, two battalions were sent to help defend Hong Kong (then a British colony), but the results were disastrous, as the Japanese imperial forces swept to victory. An ill-planned and poorly executed raid on the German-occupied French port of Dieppe was attempted, largely by Canadian troops, in August 1942, with significant casualties. Lessons learned from the disaster, however, later proved useful during the planning for the Normandy (France) Invasion in 1944. What became known as the Battle of the Atlantic marked one of Canada’s largest commitments. Canadian escorts helped protect the convoys that traversed the Atlantic bringing supplies to Britain. Again Canada suffered many casualties, both in the naval service and in the merchant marine. Under the British Commonwealth Air Training Plan, Canadians flew in both Royal Canadian Air Force and combined Royal Air Force (RAF) squadrons from the Battle of Britain through the bombing campaigns over Germany to eventual victory. Aircrew losses were particularly heavy in the RAF Bomber Command.

At Normandy in June 1944, Canada was assigned one of the five invasion beaches. Casualties began to mount quickly as the offensive in France dragged on, and the Canadian army became strapped for infantry reinforcements. The Canadian army, which had been fighting in Sicily and Italy since July 1943, was crippled by particularly high infantry casualties in late summer and early fall 1944. King’s minister of national defense, J.L. Ralston, supported sending conscripts overseas and was forced to resign as a result. Ralston’s resignation precipitated a cabinet crisis, which was resolved in November 1944 when King relented and agreed to send conscripts to the front to reinforce the army’s infantry units.

Not only was Canada’s war effort in World War II far more extensive than that in World War I, but it also had a much more lasting impact on Canadian society. By the end of the war, more than 1,000,000 Canadians (about 50,000 of whom were women) had served in the three services, including members of Indigenous nations; Tommy Prince of the Brokenhead Ojibway Nation was one of Canada’s most-decorated Indigenous war veterans, having been awarded a total of 11 medals for his service in World War II and the Korean War. Although total casualties were lower than in the previous war, still some 42,000 were killed or died in service, and 54,400 were wounded. The domestic war effort was no less significant. Canada hosted, and paid much of the cost of, the British Commonwealth Air Training Plan, which trained more than 100,000 Commonwealth airmen. Canadian factories turned out everything from rifles to Lancaster heavy bombers, and Canadian scientists, technicians, and engineers worked on advanced weapons technology, including the atomic bomb (for which Canada supplied the uranium ore). Canadian foods, direct cash contributions to Britain, and munitions for the Allies, including the Soviet Union, contributed to the overall war effort.

The government intervened in almost all aspects of Canadian life to regulate the war effort, ensure a smooth flow of troops and supplies, and curtail inflation. Agencies such as the Wartime Prices and Trade Board and the National War Labour Board represented a massive growth in the federal government, bringing a surge of government spending and a vast increase in the civil service. Toward the end of the war, the King government launched even further social welfare policies, introducing a major veterans’ benefits program, family allowances, farm price supports, compulsory collective bargaining, and a national housing program. It would undoubtedly have gone even further than it did in 1945 and 1946—a national health insurance plan was under consideration—but for the opposition of provincial governments, particularly Ontario and Quebec. Despite that opposition, however, the war produced a significant shift of power toward Ottawa. World War II had been a watershed in Canadian history, as the role of the federal government in engineering national economic growth had been considerably strengthened.