The main reason behind the Cuban Missile Crisis in 1962 was the mounting tensions between the United States and the Soviet Union, particularly regarding nuclear weapons. The crisis erupted when U.S. reconnaissance flights revealed that the Soviet Union was installing nuclear missile sites in Cuba, just 90 miles from the U.S. mainland. This action intensified fears in the U.S. about national security and the potential for a nuclear war. President John F. Kennedy faced immense pressure to respond decisively while avoiding escalation. The standoff ultimately led to a tense 13-day diplomatic crisis, which ended with the Soviet withdrawal of missiles from Cuba in exchange for a U.S. pledge not to invade the island and the removal of U.S. missiles from Turkey.