|4 August 1914
||Britain declared war on Germany, making Canada a belligerent in the First World War. Initially, the US declared neutrality, a position that many Canadians resented. After the Americans entered the war in April 1917, relations between Canada and the United States became closer, more intense, and more complex.
|1 November 1924
||The Boston Bruins became the first US team in the National Hockey League. Within two years, five other American squads joined. By 1926, there were ten teams, of which only four were Canadian. There was little handwringing over the entry of American teams, as it was necessary to prevent the creation of a better-funded all-American league, against which the NHL would not have been able to compete for players.
|17 June 1930
||President Herbert Hoover signed the Smoot–Hawley Tariff into law. The governments of both Canada and the United States reacted to the Great Depression by increasing tariffs, an approach that only made matters worse. Canadian exports to the United States dropped dramatically.
|26 May 1932
||Parliament passed the Canadian Radio Broadcasting Act, which created the Canadian Radio Broadcasting Commission. It became the Canadian Broadcasting Corporation (CBC) in 1936. The company was the government’s response to fears that Americans would dominate Canadian airwaves if the government did not intervene.
|4 March 1933
||Franklin Roosevelt became president of the United States. He was highly popular throughout Canada, where he was known for his radio addresses. In 1935, Prime Minister R.B. Bennett attempted to salvage his government by implementing a Canadian New Deal, a close imitation of Roosevelt’s program.
|9 November 1935
||Canada and the US signed a trade agreement. Prime Minister Mackenzie King had returned to office just weeks earlier and quickly negotiated the pact with the United Sates, the first since the Reciprocity Treaty of 1854. The tariff reductions were slight, but did mark the end of the National Policy era. In 1938, a more extensive trade agreement further reduced tariffs between Canada and the United States.
|11 March 1941
||An international tribunal issued its final report on the Trail smelter. Emissions from the smelter in Trail, BC, had long damaged crops, orchards, and grazing lands in Washington State. Under the tribunal’s report, farmers received compensation for damages caused by the smelter, and the owners undertook to control the emissions. One of the most-cited rulings in international environmental law, the report established the principal that no country had the right to use its territory, or allow others to use its territory, in such a way that emissions could cause damage to territory or property in another country.