The arms race between the United States and the Soviet Union probably began as soon as the Soviets heard about the mushroom cloud over Hiroshima. In 1949, the Soviets—who had been working frantically to catch up with the Americans' nuclear technologies—detonated their first atomic bomb, and throughout the 1950s the two nations raced to build ever-growing stockpiles of nuclear weapons. By the 1960s, however, both sides began to question whether continuing to build their nuclear arsenals was really beneficial. Each country had enough weapons to destroy the other multiple times over—the US possessed around 30,000 nuclear warheads while the Soviets had about 5,000. Under President Dwight Eisenhower, Secretary of State John Foster Dulles had developed the policy of "massive retaliation," whereby nuclear weapons' real power was to deter attacks; Dulles reasoned that no nation would want to risk "massive retaliation" with nuclear weapons by attacking American interests abroad. President Lyndon Johnson's Secretary of State, Robert McNamara, built upon Dulles's ideas of deterrence to develop the policy of "Mutual Assured Destruction": if both Americans and Soviets adopted a policy of massive retaliation, and if both maintained a large enough nuclear arsenal to ensure each other's complete annihilation in the event of nuclear war, then the consequences of nuclear war would be so high that neither would ever launch a nuclear attack. Thus the Mutual Assured Destruction inherent in nuclear war would forever deter either side from ever starting one. Huge arsenals of nuclear weapons, paradoxically, were the only thing that could be depended upon to save the world from destruction by huge arsenals of nuclear weapons.
Many critics seized upon Mutual Assured Destruction's unfortunate acronym—MAD—to decry the policy a form of institutionalized madness, perpetuating a worldwide "balance of terror" that would forever threaten to end human civilization via nuclear holocaust. While the critics had a point—on several occasions since 1945 nuclear weapons have come terrifyingly close to being used, either by accident or miscalculation—anti-nuclear activists have never been able to develop a credible strategy for stuffing the nuclear genie back into the bottle. Mad as it may have been, MAD did succeed in its most basic objective: the Soviet Union and United States never destroyed each other in nuclear war.
Surprisingly, perhaps, MAD led by the mid-1960s to the first successful nuclear arms control agreements. Once both sides possessed enough warheads to destroy each other completely, there was no need to continue racing to build ever-larger nuclear arsenals. After all, what was the point of being able to destroy the entire world many times over? After growing quickly throughout the 1950s and early 1960s, the American nuclear stockpile actually shrank slowly from a peak of 31,323 warheads in 1966 to 23,387 by 1980.
The Cuban Missile Crisis of 1962 demonstrated with horrifying clarity the dangers of nuclear proliferation (the spread of nuclear weapons to more and more countries). American President John F. Kennedy and Soviet Premier Nikita Khrushchev were able to stave off disaster through negotiation, but at the height of the crisis Cuban leader Fidel Castro actually pushed hard to launch a nuclear strike against the United States. If the weapons had been under Castro's operational control, rather than Khrushchev's, we might all be dead.
In 1963, in the immediate wake of the Missile Crisis, the leaders of the United States, Soviet Union, and Great Britain joined together to sign the Limited Test Ban Treaty, which they hoped would slow new development of nuclear weapons technology by banning test explosions in the atmosphere. More than 105 other nations signed on, though Cuba, China, and France all refused to join. While all three of those nations were allied with nuclear powers (the US in the case of France, the USSR in the case of Cuba and China), all three felt that only by controlling their own nuclear arsenals could they maintain their independence in world affairs.
France obtained the bomb in 1960, and China followed quickly after. While Chairman Mao had once dismissed the atom bomb as nothing more than a "paper tiger"—a weapon that looked fearsome but was worthless in battle—by the 1960s China desperately hoped to join the ranks of the nuclear powers. In 1964 Chinese scientists successfully detonated their first bomb.
The proliferation of nuclear technology to France and China only intensified American, British, and Soviet efforts to prevent even more countries from obtaining the bomb. In 1968, the United States, Great Britain, and the Soviet Union signed the Nuclear Non-Proliferation Treaty, agreeing not to distribute nuclear weapons to other nations and to limit the development of nuclear delivery systems. The treaty opened each country's nuclear facilities to inspections by the United Nations' International Atomic Energy Agency. The Nixon administration met with the Soviets in Helsinki, Finland, in 1969 to begin discussing further limits on nuclear weapons. These talks led to the 1972 Strategic Arms Limitation Treaty (SALT I), which froze the number of nuclear missiles (ICBMs) on both sides at current levels for five years. These agreements limiting nuclear weapons contributed greatly to détente (the relaxation of Cold War tensions) during this period. Nixon's successor as president, Gerald Ford, met with Khrushchev's successor, Leonid Brezhnev, in Siberia at Vladivostok to discuss more arms control. Ford laid the groundwork for SALT II, a second treaty which would be signed by Brezhnev and President Jimmy Carter in Vienna a few years later.