Final answer:
The Cuban Missile Crisis in 1962 was the closest the world has come to nuclear war, with the U.S. and the Soviet Union nearly engaging in conflict over Soviet missiles in Cuba. It led to the establishment of a direct hotline between the two superpowers and the signing of the Limited Test Ban Treaty to prevent such crises in the future.
Step-by-step explanation:
The closest that the world came to an all-out nuclear war was during the Cuban Missile Crisis. This was a tense diplomatic confrontation in October 1962 between major world powers. The United States and the Soviet Union nearly engaged in nuclear conflict over the deployment of Soviet missiles in Cuba. During those 13 days, the world was on the brink of nuclear war as both sides had nuclear weapons ready to launch. Fortunately, through intense negotiations, President John F. Kennedy and Soviet Premier Nikita Khrushchev reached an agreement to remove nuclear missiles from locations near each other's borders, averting a catastrophic nuclear confrontation.
Following this crisis, both nations took steps to reduce the risk of such a near-miss happening again, including establishing a direct telephone hotline between Washington and Moscow. The Limited Test Ban Treaty was also signed in 1963, banning nuclear weapons tests in the atmosphere.