The Cuban Missile Crisis was a 13-day confrontation between the United States and the Soviet Union, widely considered the moment the world came closest to nuclear war. The crisis began when U.S. spy planes discovered Soviet nuclear missile sites being constructed in Cuba, just 90 miles from the Florida coast. President John F. Kennedy enacted a naval 'quarantine' of the island to prevent further shipments. For two weeks, the world watched as the two superpowers engaged in a tense standoff. The crisis was eventually resolved when Soviet leader Nikita Khrushchev agreed to remove the missiles in exchange for a public U.S. promise not to invade Cuba and a secret agreement to remove U.S. missiles from Turkey. The event led to the establishment of the 'hotline' between Washington and Moscow and pushed both nations toward the first steps of nuclear arms control.