The Cold War was a period of diplomatic and political tension between the United States and Soviet Union from 1945-1991. Key events included the spread of communism in countries like China and Cuba, the Truman Doctrine and Marshall Plan which aimed to contain communism, and conflicts like the Korean War and Vietnam War where the two superpowers supported opposing sides. The arms race led to massive military buildups and a space race, raising fears of nuclear war. Ultimately, economic and political pressures contributed to the dissolution of the Soviet Union in the late 1980s, marking a U.S. victory in the Cold War.