The Cold War

Following Germany's surrender in May 1945, near the end of World War II, the tense wartime alliance between the US and the UK on one hand, and the Soviet Union on the other, began to disintegrate. 

By 1948, the Soviets had installed left-wing governments in countries freed by the Red Army in Eastern Europe. The United States and the United Kingdom feared permanent Soviet dominance in Eastern Europe, as well as the possibility of Soviet-influenced communist parties gaining power in Western Europe's democracies.

The Soviets, on the other hand, were hell-bent on maintaining control of eastern Europe in order to protect themselves from a resurgent German threat, and they were hell-bent on spreading communism throughout the world, partly for ideological reasons. 

By 1947–48, the Cold War had entrenched, with US aid to western Europe under the Marshall Plan bringing those countries under American control and the Soviets installing openly communist regimes in eastern Europe.

In 1948–53, the Cold War reached its pinnacle. During this time, the Soviets tried unsuccessfully to blockade the Western-held sectors of West Berlin (1948–49); in 1949, the US and its European allies formed the North Atlantic Treaty Organization, a unified military command to combat the Soviet presence in Europe; in 1949, the Soviets exploded their first atomic warhead, ending the American monopoly on the atomic bomb; and in 1949, the Chinese communists exploded their first atomic warhead, effectively ending the American monopoly.

Cold War tensions eased slightly from 1953 and 1957, owing in part to the death of long-serving Soviet autocrat Joseph Stalin in 1953. 

In 1955, the Warsaw Pact, a united military organization of Soviet-bloc countries, was founded, and West Germany was admitted to NATO the same year. In 1958–62, the Cold War was at its most intense. 

The US and the Soviet Union began working on intercontinental ballistic missiles, and the Soviets began surreptitiously deploying missiles in Cuba in 1962 that could be used to conduct nuclear assaults on US cities.

During the Cold War, the US and the Soviet Union avoided direct military conflict in Europe and only engaged in combat operations to prevent allies from defecting to the opposing side or to overthrow them after they had done so. As a result, the Soviet Union sent soldiers to East Germany in 1953, Hungary in 1956, Czechoslovakia in 1968, and Afghanistan in 1979 to maintain communist control.

For its part, the US assisted in the overthrow of a left-wing government in Guatemala in 1954, supported an unsuccessful invasion of Cuba in 1961, invaded the Dominican Republic in 1965 and Grenada in 1983, and attempted but failed to prevent communist North Vietnam from annexing South Vietnam.

The Cuban missile crisis demonstrated that neither the US nor the Soviet Union were willing to deploy nuclear weapons for fear of retaliation from the other, resulting in mutual atomic destruction. 

The Nuclear Test-Ban Treaty of 1963, which prohibited aboveground nuclear weapons testing, was quickly signed by the two superpowers. The crisis, however, sharpened the Soviets' resolve to never be humiliated by their military inferiority again, and they began a buildup of conventional and strategic forces that the US was obliged to match for the following 25 years.

However, over the 1960s and 1970s, the bipolar battle between the Soviet and American blocs gave way to a more complex pattern of international relations, in which the globe was no longer divided into two obviously opposed blocs. 

The Soviet Union and China suffered a fundamental schism in 1960 that worsened over the years, destroying the communist bloc's cohesiveness. Meanwhile, in the 1950s and 1960s, Western Europe and Japan had rapid economic growth, lowering their relative disadvantage to the United States. 

Less powerful countries were given more leeway to declare their independence, and they frequently demonstrated their resistance to superpower coercion.

The Strategic Arms Limitation Talks (SALT) that led to the SALT I and II agreements of 1972 and 1979, respectively, saw an easing of Cold War tensions, as evidenced by the Strategic Arms Limitation Talks (SALT) that led to the SALT I and II agreements of 1972 and 1979, in which the two superpowers set limits on their antiballistic missiles and strategic missiles capable of carrying nuclear weapons. 

In the early 1980s, the two superpowers resumed their major military buildup and battled for influence in the Third World, resulting in renewed Cold War tensions. However, during the administration of Soviet leader Mikhail S. Gorbachev in the late 1980s, the Cold War began to break down.

He initiated efforts to democratize the Soviet political system by dismantling the dictatorial characteristics of the Soviet system. Gorbachev acquiesced in the breakdown of communist regimes in the Soviet-bloc nations of eastern Europe in 1989–90. 

The ascension to power of democratic administrations in East Germany, Poland, Hungary, and Czechoslovakia was swiftly followed by the unification of West and East Germany under NATO auspices, with Soviet approval once more.

In the meantime, Gorbachev's internal reforms had weakened his own Communist Party, allowing authority to pass to Russia and the other Soviet republics. The Soviet Union fell in late 1991, leaving 15 newly independent states in its wake, including a Russia led by a freely elected anticommunist president.