Four years after the United States exploded the first atomic bomb, the Soviet Union tested their own. With this, the arms race between America and the Soviet Union began.
The arms race was a cycle of military buildup. When one nation (usually the United States) developed a new military technology or increased its number of nuclear weapons, the other would catch up. Once this nation matched or bested its opponent's capabilities, the first nation would start the cycle again in order to ensure their security.
One reason for arms buildup was fear of a "Missile Gap." For a period of time, some in the United States feared that the Soviet Union possessed equal or greater numbers of nuclear weapons than the U.S. Soviet Premier Nikita Khrushchev boasted of the Soviet Union's quantity of nuclear arms. This was, however, disproved by American reconnaissance.
Another reason for arms buildup was to maintain formidable status. A large number of nuclear weapons could be considered sufficient deterrance to any enemy nation. It was hoped that the threat of a nuclear holocaust would be enough to ensure that nuclear weapons would be unused.
As the Cold War progressed, proposals began for arms reduction. In September 1961, the United States formed the Arms Control and Disarmament Agency, which dealt with government policy concerning nuclear testing and arms control. In May 1972, the first of the Strategic Arms Limitation Talks (SALT I) came to end in the form of a treaty between the U.S. and the U.S.S.R. to limit their anti-ballistic missile systems. Since neither nation trusted the other, their reconnaissance programs played a key role in the decisions of both countries. SALT I took the first step in mutual arms control agreements between America and the Soviet Union. Since that time, many other arms control treaties have followed.