Occurred in 1962 as a result of conflict between the United States and the Soviet Union. The United States had deployed nuclear missiles all around the Soviet Union, most threateningly in Turkey. Meanwhile, Fidel Castro was worried about an American invasion of Cuba. He requested that the Soviet Union place nuclear missiles in Cuba, thinking that this would prevent an invasion. On October 14, 1962, an American U-2 spying on Cuba spotted the missile installations. U.S. President John F. Kennedy was informed, and a debate as to how to react ensued among the American leadership. Most of Kennedy's advisors wanted to invade Cuba immediately or bomb the missile sites. Kennedy objected to this. In since declassified tapes of the conversation, Kennedy stated his opinion that the missiles added nothing to the Soviet's military capabilities.
Kennedy used the crisis as a political tool. His approach was one of strength and resoluteness towards the nuclear threat. About a week after spotting the missile sites, Kennedy ordered a naval blockade of Cuba. This was meant to prevent ships with more missiles from reaching the island. At the same time, the US brought its nuclear arsenal to full wartime readiness.
On October 26, American nuclear bombers flew past their turnaround points and invaded Soviet airspace. At that point, fearing a nuclear war, Khrushchev agreed to remove the missiles. In return, the United States promised not to invade Cuba and removed some of its missiles from Turkey. The no-invasion promise still stands today. The next day an American U-2 was again spotted over Cuba. It was shot down, leading to the crisis' only casualty. The situation was very delicate to say the least. Had American forces invaded, a nuclear war would likely have started. The Soviets placed short range nuclear missiles in Cuba that probably would have been used on the invaders to defend the island. Kennedy had promised that a nuclear attack from Cuba would be interpreted as a nuclear attack by the USSR, meaning that such a Cuban attack could have lead to full-scale nuclear war.
With many thanks to the students project of Thinkquest