In 1945, just before the end of World War II, the leaders of the main Allied countries (the United States, the U.S.S.R and Britain) held a conference at Yalta to discuss post-war relations. When the war ended, the Red Army occupied much of Eastern Europe. The evident weakness of Western Europe raised the specter of communism spreading even further.

Although the Marshall Plan helped restore Western Europe, other events of the late 1940s kept tension high: the Communist coup in Czechoslovakia and Soviet blockade of West Berlin in 1948, the fall of China and the Soviet A-bomb in 1949. Soviet support for the North Korean invasion of South Korea in 1950 confirmed the threat in Western eyes.

The establishment in 1949 of the Western alliance, NATO (North Atlantic Treaty Organization), and the 1955 Warsaw Pact between the Soviet Union and its satellites solidified the two opposing blocs that shaped the Cold War.

The threat of nuclear annihilation restrained the armed forces of the United States and the Soviet Union from directly confronting each other in battle. The closest call came in 1962, when the Soviet Union secretly placed offensive missiles with nuclear warheads in Cuba, and provoked an American naval quarantine that brought the two superpowers to the brink of war. For the most part, the superpowers fought by subverting unfriendly regimes or covertly arming surrogate forces. Both sides regularly provided military advisors to countries or factions they supported.

Throughout the 1980s, the Soviet Union fought an increasingly frustrating war in Afghanistan. At the same time, the Soviet economy faced the continuously escalating costs of the arms race. Dissent at home grew while the stagnant economy faltered under the combined burden. Attempted reforms at home left the Soviet Union unwilling to rebuff challenges to its control in Eastern Europe. During 1989 and 1990, the Berlin Wall came down, borders opened, and free elections ousted Communist regimes everywhere in eastern Europe. In late 1991 the Soviet Union itself dissolved into its component republics. With stunning speed, the Iron Curtain was lifted and the Cold War came to an end.