WWII started in 1939 by the invasion of Poland from the Germans is one of the causes of WWII but also the attacks from Japan toward China, USA and the Britannic colonies. Also the failure of League of Nations, Failure of Treaty of Versailles, the Failure appeasement and the rise of Hitler.
No one wanted a WWII so we tried to do our best to not have war again but Germany just did to much so we got the WWII.
The prime minister from Canada was William Lyon Mackenzie King. Franklin D. Roosevelt was president of US for most of the war. He died in April of 1945 and Vice President Harry Truman became president for the last few months of war. Neville Chamberlain was prime minister of Britain in 1939 and he was the one who declared war on Germany. In 1940 Winston Churchill was selected to replace him and was prime minister until end of war. Joseph Stalin was the president from Russia, and Adolf Hitler was the president of Germany.
Also the Japanese Canadians who used to live in British Columbia during WW2. This started in December 1941. This happened because the Japanese air force attacked the American base at Pearl Harbor, Hawaii and it was justified on grounds of national security. Japan internees were given the choice of deportation or transfer to other parts of Canada.