| 5 September 1945 |
Igor Gouzenko smuggled secret documents out of the Soviet Embassy in Ottawa and later turned them over to Canadian officials. The Gouzenko Affair revealed that the Soviets were operating an espionage network in North America, news that rocked Canada and the United States. In the coming years, Canadians and Americans viewed the Cold War through similar lenses, terrified about communist subversion at home and fearful of Soviet expansionism abroad. |
| 4 April 1949 |
Canada, the United States, and ten Western European countries signed a treaty to create the North Atlantic Treaty Organization (NATO). The collective security alliance was a reaction to fears of Soviet expansion in Europe. |
| 25 June 1950 |
Communist North Korea invaded South Korea, marking the beginning of the Korean War. The US decided to send troops to defend the south, as did Canada. Hostilities ended with an armistice in July 1953. |
