The Cold War was a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term cold war is used because there was no large-scale fighting directly between the two superpowers, but they each supported opposing sides in major regional conflicts known as proxy wars. The conflict was based on the ideological and geopolitical struggle for global influence by these two superpowers, following their roles as the Allies of World War II that led to victory against Nazi Germany and Imperial Japan in 1945. Aside from the nuclear arms race and conventional military deployment, the struggle for dominance was expressed via indirect means, such as psychological warfare, propaganda campaigns, espionage, far-reaching embargoes, sports diplomacy, and technological competitions like the Space Race. The Cold War began shortly after the end of World War II, started a gradual winding down with the Sino-Soviet split between the Soviets and the People's Republic of China in 1961, and ended with the collapse of the Soviet Union in 1991.
The Western Bloc was led by the United States, as well as a number of other First World nations that were generally liberal democratic but tied to a network of often authoritarian, Third World states, most of which were the European powers' former colonies. The Eastern Bloc was led by the Soviet Union and its Communist Party, which had an influence across the Second World and was also tied to a network of authoritarian states. The Soviet Union had a command economy and installed similarly Communist regimes in its satellite states. United States involvement in regime change during the Cold War included support for anti-communist and right-wing dictatorships, governments, and uprisings across the world, while Soviet involvement in regime change included the funding left-wing parties, wars of national liberation and revolutions around the world. As nearly all the colonial states underwent decolonization and achieved independence in the period from 1945 to 1960, many became Third World battlefields in the Cold War.
The first phase of the Cold War began shortly after the end of World War II in 1945. The United States and its Western European allies sought to strengthen their bonds and used the policy of containment against Soviet influence; they accomplished this most notably through the formation of NATO, which was essentially a defensive agreement in 1949. The Soviet Union countered with the Warsaw Pact in 1955, which had similar results with the Eastern Bloc. As by that time the Soviet Union already had an armed presence and political domination all over its eastern satellite states, the pact has been long considered superfluous. Although nominally a defensive alliance, the Warsaw Pact's primary function was to safeguard Soviet hegemony over its Eastern European satellites, with the pact's only direct military actions having been the invasions of its own member states to keep them from breaking away; in the 1960s, the pact evolved into a multilateral alliance, in which the non-Soviet Warsaw Pact members gained significant scope to pursue their own interests. In 1961, Soviet-allied East Germany constructed the Berlin Wall to prevent the citizens of East Berlin from fleeing to West Berlin, at the time part of United States-allied West Germany. Major crises of this phase included the Berlin Blockade of 1948–1949, the Chinese Communist Revolution of 1945–1949, the Korean War of 1950–1953, the Hungarian Revolution of 1956 and the Suez Crisis of that same year, the Berlin Crisis of 1961, the Cuban Missile Crisis of 1962, and the Vietnam War of 1964–1975. Both superpowers competed for influence in Latin America and the Middle East, and the decolonising states of Africa, Asia, and Oceania.