The Soviet ship Poltava heads toward Cuba, one of the events that sets into motion the Cuban Missile Crisis.

The Cuban Missile Crisis, also known as the October Crisis of 1962 (Spanish: Crisis de Octubre), the Caribbean Crisis (Russian: , tr. Karibsky krizis, IPA: [kripskj krizs]), or the Missile Scare, was a 35-day (16 October 20 November 1962) confrontation between the United States and the Soviet Union, which escalated into an international crisis when American deployments of missiles in Italy and Turkey were matched by Soviet deployments of similar ballistic missiles in Cuba. Despite the short time frame, the Cuban Missile Crisis remains a defining moment in US national security and nuclear war preparation. The confrontation is often considered the closest the Cold War came to escalating into a full-scale nuclear war.In response to the presence of American Jupiter ballistic missiles in Italy and Turkey, and the failed Bay of Pigs Invasion of 1961, Soviet First Secretary Nikita Khrushchev agreed to Cuba's request to place nuclear missiles on the island to deter a future invasion. An agreement was reached during a secret meeting between Khrushchev and Cuban Prime Minister Fidel Castro in July 1962, and construction of a number of missile launch facilities started later that summer.

Meanwhile, campaigning for the 1962 United States elections was underway, and the White House denied charges for months that it was ignoring dangerous Soviet missiles 90 mi (140 km) from Florida. The missile preparations were confirmed when a US Air Force U-2 spy plane produced clear photographic evidence of medium-range R-12 (NATO code name SS-4) and intermediate-range R-14 (NATO code name SS-5) ballistic missile facilities.

When this was reported to President John F. Kennedy, he then convened a meeting of the nine members of the National Security Council and five other key advisers, in a group that became known as the Executive Committee of the National Security Council (EXCOMM). During this meeting, President Kennedy was originally advised to carry out an air strike on Cuban soil in order to compromise Soviet missile supplies, followed by an invasion of the Cuban mainland. After careful consideration, President Kennedy chose a less aggressive course of action, in order to avoid a declaration of war. After consultation with EXCOMM, Kennedy ordered a naval "quarantine" on October 22 to prevent further missiles from reaching Cuba. By using the term "quarantine", rather than "blockade" (an act of war by legal definition), the United States was able to avoid the implications of a state of war. The US announced it would not permit offensive weapons to be delivered to Cuba and demanded that the weapons already in Cuba be dismantled and returned to the Soviet Union.

After several days of tense negotiations, an agreement was reached between Kennedy and Khrushchev: publicly, the Soviets would dismantle their offensive weapons in Cuba and return them to the Soviet Union, subject to United Nations verification, in exchange for a US public declaration and agreement to not invade Cuba again. Secretly, the United States agreed with the Soviets that it would dismantle all of the Jupiter MRBMs which had been deployed to Turkey against the Soviet Union. There has been debate on whether or not Italy was included in the agreement as well. While the Soviets dismantled their missiles, some Soviet bombers remained in Cuba, and the United States kept the naval quarantine in place until November 20, 1962.When all offensive missiles and the Ilyushin Il-28 light bombers had been withdrawn from Cuba, the blockade was formally ended on November 20. The negotiations between the United States and the Soviet Union pointed out the necessity of a quick, clear, and direct communication line between the two superpowers. As a result, the MoscowWashington hotline was established. A series of agreements later reduced USSoviet tensions for several years, until both parties eventually resumed expanding their nuclear arsenals.

The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was a communist state that spanned Eurasia from 1922 to 1991. It was nominally a federal union of multiple national republics; in practice its government and economy were highly centralized until its final years. The country was a one-party state (prior to 1990) governed by the Communist Party of the Soviet Union, with Moscow as its capital within its largest and most populous republic, the Russian SFSR. Other major urban centers were Leningrad (Russian SFSR), Kiev (Ukrainian SSR), Minsk (Byelorussian SSR), Tashkent (Uzbek SSR), Alma-Ata (Kazakh SSR) and Novosibirsk (Russian SFSR). It was the largest country in the world, covering over 22,402,200 square kilometres (8,649,500 sq mi), and spanning eleven time zones.

The Soviet Union had its roots in the October Revolution of 1917 when the Bolsheviks, headed by Vladimir Lenin, overthrew the Provisional Government that had earlier replaced the house of Romanov of the Russian Empire. They established the Russian Soviet Republic, the world's first constitutionally guaranteed socialist state. Tensions escalated into a civil war between the Bolshevik Red Army and many anti-Bolshevik forces across the former Empire, among whom the largest faction was the White Guard. The White Guard engaged in violent anti-communist repression against the Bolsheviks and suspected worker and peasant Bolsheviks known as the White Terror. The Red Army expanded and helped local Bolsheviks take power, establishing soviets, repressing their political opponents and rebellious peasants through Red Terror. By 1922, the balance of power had shifted and the Bolsheviks had emerged victorious, forming the Soviet Union with the unification of the Russian, Transcaucasian, Ukrainian and Byelorussian republics. Upon the conclusion of the civil war Lenin's government introduced the New Economic Policy, which led to a partial return of a free market and private property; this resulted in a period of economic recovery.

Following Lenin's death in 1924, Joseph Stalin came to power. Stalin suppressed all political opposition to his rule inside the Communist Party and inaugurated a command economy. As a result, the country underwent a period of rapid industrialization and forced collectivization, which led to significant economic growth, but also led to a man-made famine in 1932–1933. The Gulag labour camp system was also expanded in this period. Stalin also fomented political paranoia and conducted the Great Purge to remove his actual and perceived opponents from the Party through mass arrests of military leaders, Communist Party members, and ordinary citizens alike, who were then sent to correctional labor camps or sentenced to death.

On 23 August 1939, after unsuccessful efforts to form an anti-fascist alliance with Western powers, the Soviets signed a non-aggression pact with Nazi Germany. After the start of World War II, the formally neutral Soviets invaded and annexed territories of several Eastern European states, including the eastern regions of Poland, Lithuania, Latvia and Estonia. In June 1941 the Germans invaded, opening the largest and bloodiest theater of war in history. Soviet war casualties accounted for the majority of Allied casualties of the conflict in the process of acquiring the upper hand over Axis forces at intense battles such as Stalingrad. Soviet forces eventually captured Berlin and won World War II in Europe on 9 May 1945. The territory overtaken by the Red Army became satellite states of the Eastern Bloc. The Cold War emerged in 1947, where the Eastern Bloc confronted the Western Bloc, which would unite in the North Atlantic Treaty Organization in 1949.

Following Stalin's death in 1953, a period known as de-Stalinization and the Khrushchev Thaw occurred under the leadership of Nikita Khrushchev. The country developed rapidly, as millions of peasants were moved into industrialized cities. The USSR took an early lead in the Space Race with the first ever satellite and the first human spaceflight and the first probe to land on another planet, Venus. In the 1970s, there was a brief détente of relations with the United States, but tensions resumed when the Soviet Union deployed troops in Afghanistan in 1979. The war drained economic resources and was matched by an escalation of American military aid to Mujahideen fighters.

In the mid-1980s, the last Soviet leader, Mikhail Gorbachev, sought to further reform and liberalize the economy through his policies of glasnost and perestroika. The goal was to preserve the Communist Party while reversing economic stagnation. The Cold War ended during his tenure and in 1989, Warsaw Pact countries in Central and Eastern Europe overthrew their respective Marxist-Leninist regimes. Strong nationalist and separatist movements broke out across the USSR. Gorbachev initiated a referendum—boycotted by Lithuania, Latvia, Estonia, Armenia, Georgia, and Moldova — which resulted in the majority of participating citizens voting in favor of preserving the Union as a renewed federation. In August 1991, a coup d'état was attempted by Communist Party hardliners. It failed, with Russian President Boris Yeltsin playing a high-profile role in facing down the coup. The main result was the banning of the Communist Party. The republics, led by Russia and Ukraine, declared independence. On 25 December 1991, Gorbachev resigned. All the republics emerged from the dissolution of the Soviet Union as independent post-Soviet states. The Russian Federation (formerly the Russian SFSR) assumed the Soviet Union's rights and obligations and is recognized as its continued legal personality in world affairs.

The Soviet Union produced many significant social and technological achievements and innovations regarding military power. It boasted the world's second-largest economy and the largest standing military in the world. The USSR was recognized as one of the five nuclear weapons states. It was a founding permanent member of the United Nations Security Council as well as a member of the OSCE, the WFTU and the leading member of the Council for Mutual Economic Assistance and the Warsaw Pact.

Before its dissolution, the USSR had maintained its status as a superpower, alongside the United States, for four decades after World War II. It exercised its hegemony in East-Central Europe and worldwide with military and economic strength, proxy conflicts and influence in developing countries and funding of scientific research, especially in space technology and weaponry.