During World War II, the United States and the Union of Soviet Socialist Republics (USSR) had been allies. After the war, however, divergent ideological and economic systems and competing geopolitical interests fueled a conflict between the former allies that was quickly dubbed the “Cold War.” This “war” began in the immediate postwar years. As Soviet leader Joseph Stalin sought to expand the USSR's sphere of influence in Eurasia, the United States responded with multiple economic and military “containment” policies. The Cold War continued for decades and ended with the demise of the Soviet Union in 1991, following the steady decrease in the influence of the Communist Party of the Soviet Union (CPSU) under the leadership of Mikhail Gorbachev and his reform programs of perestroika (restructuring) and glasnost (openness or transparency), which encouraged democratic forces in Russia and other Soviet satellite nations.
The main players, the United States and Soviet Union, were hardly the only nations affected by the Cold War. The two superpowers drew multiple African, Latin American, Asian, Southeast Asian, and European countries into their conflict. In particular, the contest between U.S. and Soviet nuclear power that characterized the Cold War made this conflict supremely relevant and perilous for nations the world over. Additionally, the U.S. and the Soviet Union each provided financial, military, and political support to friendly governments engaged in wars that served their respective interests, either containing or spreading communism. These “proxy wars” included the Korean War, Suez Crisis, Congolese Crisis, Angolan Civil War, Ethiopian Crisis, Nicaraguan Revolution, Salvadoran Civil War, Soviet-Afghan War, and, most notably, the Vietnam War. In addition to proxy wars, key forces and events that defined the Cold War included: postwar division and occupation of Germany and Berlin; erection of the Berlin Wall in 1961; the 1962 Cuban Missile Crisis; establishment of key American defense institutions, including the Central Intelligence Agency (CIA), National Security Agency (NSA), and National Aeronautics and Space Administration (NASA); establishment of international military alliances, including the North Atlantic Treaty Organization (NATO), the Southeast Asia Treaty Organization (SEATO), the Central Treaty Organization (CENTO), the Association of Southeast Asian Nations (ASEAN), and the Warsaw Pact; nuclear arms and space races; the Strategic Arms Limitation Talks and Treaties; and the fall of the Berlin Wall (1989).