Great Britain declared war on Germany on August 4, 1914. Because the country was under the dominion of the British Empire, Canada automatically became involved. However, the next day the Canadian Governor General officially declared war on Germany due to the overwhelming support of the country's citizens. (The majority of these were of British descent.)
The War Measures Act was both adopted and enacted during the first year of the war. This statue gave the Canadian government "sweeping powers" in times of emergency, to include war. Almost four years later the statute was altered to give the government even more authority in response to the Russian Revolution in 1917.