The crisis began when the Soviet Union secretly began to install nuclear missiles in Cuba, just 90 miles from the U.S. coast.

Soviet leader Nikita Khrushchev's motivations included protecting communist Cuba from a U.S. invasion and countering the presence of U.S. missiles in Turkey.

In October 1962, U.S. U-2 spy planes discovered the missile sites, triggering a tense 13-day standoff between the U.S. and the USSR.

This is considered the closest the world has ever come to a full-scale nuclear war.

U.S. President John F. Kennedy and his advisors debated a response, ranging from an air strike to a full-scale invasion.

Kennedy chose to implement a naval 'quarantine' (a blockade) around Cuba to prevent more missiles from arriving.

The world watched anxiously as Soviet ships approached the quarantine line.

The crisis was ultimately resolved through intense secret negotiations between Kennedy and Khrushchev.

The deal involved the Soviets removing the missiles from Cuba in exchange for a U.S. pledge not to invade Cuba.

The U.S. also secretly agreed to remove its missiles from Turkey at a later date, and the crisis led to the establishment of the Moscow-Washington hotline.