In the late 1950s, both the United States and the Soviet Union were developing intercontinental ballistic missiles. In 1962 the Soviet Union began to secretly install missiles in Cuba to launch attacks on U.S. cities. The confrontation that followed, known as the Cuban missile crisis, brought the two superpowers to the brink of war before an agreement was reached to withdraw the missiles.
The conflict showed that both superpowers were wary of using their nuclear weapons against each other for fear of mutual atomic annihilation. The signing of the Nuclear Test-Ban Treaty followed in 1963, which banned aboveground nuclear weapons testing. Still, after the crisis, the Soviets were determined not to be humiliated by their military inferiority again, and they began a buildup of conventional and strategic forces that the United States was forced to match for the next 25 years.