Final answer:
The Cuban Missile Crisis began when the United States discovered the U.S.S.R. was installing nuclear missiles in Cuba, leading to a tense 13-day standoff during President Kennedy's tenure. This confrontation nearly escalated into nuclear war but ended peacefully through diplomatic negotiations.
Step-by-step explanation:
The Cuban Missile Crisis began when the United States discovered that the U.S.S.R. was installing offensive nuclear weapons in Cuba. This incident notably occurred under the administration of President John F. Kennedy, not President Johnson, in October of 1962. Soviet Premier Nikita Khrushchev had reached an agreement with Cuban leader Fidel Castro to place nuclear missiles on Cuban soil, aimed at deterring another US invasion following the failed Bay of Pigs Invasion.
Reconnaissance flights provided the United States with photographic evidence of these missile installations, leading to a tense 13-day standoff. The resolution of the crisis involved a secret agreement, where the United States agreed to remove its nuclear missiles from Turkey, while the Soviet Union removed theirs from Cuba. This tense period is marked in history as a pivotal moment when the Cold War could have escalated into nuclear warfare but was ultimately resolved through diplomatic channels.