The long-term cause of the Cuban Missile Crisis had to do with the distrust between the United States and the Soviet Union at the end of World War II. Although they had fought as allies, when the war was over, the two countries were hostile towards each other. The United States feared worldwide communist domination, and the USSR resented the US approach to foreign relations, which it perceived as interventionist.
This conflict became known as the Cold War. In the years following World War II, especially after 1949 when the Soviets first tested an atomic bomb, it turned into an arms race. Each feared the other might initiate nuclear warfare, and so each developed larger and larger arsenals of nuclear weapons.
In 1959, Fidel Castro became the leader of Cuba and aligned the Caribbean island nation with the Soviet Union. The Soviets began supplying Cuba with economic and military aid. The Americans had already installed nuclear weapons with the ability to reach the Soviet Union in Western Europe and in Turkey, so Soviet premier Nikita Khrushchev decided to counter this move by installing nuclear missiles in Cuba. The United States had already launched one failed invasion of Cuba, and Khrushchev reasoned that missiles on the island would deter future attacks.
An American spy plane flying over Cuba on October 14, 1962, took a photograph of the construction of a ballistic missile installation, and President John F. Kennedy and his advisors went on high alert. Several plans were proposed, including an invasion of Cuba. However, Kennedy took the more moderate approach of a naval blockade or quarantine of the island. On October 22, 1962, he informed the American people about what was happening. He warned that the United States would use military force to prevent any ships bearing weapons from reaching Cuba.
The subsequent days were filled with apprehension. Many people feared that this impasse was going to lead to nuclear war. Kennedy and Khrushchev sent messages back and forth trying to put an end to the crisis. Khrushchev finally agreed to withdraw the missiles from Cuba in exchange for Kennedy's promise that the United States would not attack Cuba. Kennedy also secretly agreed to remove the US missiles from Turkey.
As a result of the Cuban Missile Crisis, the United States and the Soviet Union took certain steps to ensure that the world would never again come as close as it did to nuclear war. A telephone communication link that became known as the Hot Line was installed between the White House and the Kremlin. The two countries initiated negotiations that eventually resulted in nuclear test ban treaties. On the downside, the Soviets increased their research into intercontinental ballistic missiles that would be capable of reaching the United States from the Soviet Union.