In the midst of this crisis the Soviets unilaterally broke the moratorium on nuclear testing, staging a series of explosions yielding up to 50 megatons. Soviet technology had also perfected a smaller warhead for the new Soviet missiles now ready to be deployed, like the Minuteman, in hardened silos. Khrushchev, his nation still behind in strategic nuclear firepower, tried to redress the balance by insinuating 42 medium-range missiles into Cuba, whence they could reach most of the continental United States. He apparently hoped that these missiles, once in place, could then serve as a bargaining chip in negotiations leading to a neutralized Germany, which in turn might help Moscow persuade the Chinese to cease their own nuclear program. Instead, the ploy brought the world to the brink of war. On October 14, 1962, U-2 spy planes photographed the missile sites under construction in Cuba. Two days later Kennedy convened a secret crisis-management committee that leaned at first toward a surgical air strike to destroy the sites. The President, however, opted for a less risky response: a naval quarantine to prevent Soviet freighters from reaching Cuba and an ultimatum demanding that the bases be dismantled and the missiles removed. On October 18, Soviet Ambassador Andrey Gromyko met with Kennedy and denied that the U.S.S.R. had any offensive intentions with respect to Cuba. On October 22 the President informed the nation of the crisis and called on Khrushchev to pull back from “this clandestine, reckless, and provocative threat to world peace.” For two days the world waited anxiously, and on the 24th Soviet ships in transit abruptly changed course away from Cuba. On the 26th Khrushchev sent Kennedy a message offering to withdraw the missiles in exchange for a U.S. pledge never to invade Cuba. The next day a harsher message arrived with a new demand that the United States withdraw its own missiles from Turkey. Those antiquated Jupiters, deployed in the early post-Sputnik scare, were already due for removal, but Kennedy would not do so under Soviet threat. Hence Attorney General Robert Kennedy suggested a ploy: simply reply to Khrushchev’s first note as if the second had never been sent. On the 28th the Soviets agreed to dismantle the Cuban bases in return for a no-invasion pledge. Several months later the United States quietly removed its missiles from Turkey.

The Cuban missile crisis seemed at the time a clear victory for Kennedy and the United States and was widely attributed to American superiority in nuclear weapons. In fact, neither side showed the slightest willingness even to bluff a nuclear strike, and it was probably the overwhelming U.S. superiority in conventional naval and air power in its home waters that left the U.S.S.R. no option but retreat. Nor was the crisis an unmitigated American victory. Kennedy’s pledge never to overthrow Castro by force meant that the United States would have to tolerate whatever mischief he, backed by $300,000,000 a year in Soviet aid, might contrive in the future. To be sure, Kennedy warned that the United States would never tolerate any expansion of Communism in the hemisphere. (This pledge was underwritten by Lyndon Johnson in 1965 when he sent U.S. troops into the Dominican Republic to prevent a leftist takeover, but such interventionism only reminded Latin Americans of past “Yankee imperialism” and gave credence to Castro’s anti-American propaganda.) The existence of a Communist base in the Caribbean, therefore, was to be a source of unending vexation for future American presidents. What is more, the Cuban missile crisis hardened Soviet determination never again to be humiliated by military inferiority. Khrushchev and his successors accordingly began the largest peacetime military buildup in history, which, by the 1970s, accorded the Soviet Union parity with the United States in nuclear forces and the ability to project naval power into every ocean of the world.

On the other hand, the Cuban missile crisis marked the final frustration of Khrushchev’s efforts to force a German peace treaty and prevent the deployment of nuclear weapons on German or Chinese soil. Peking, of course, had supported the Soviets’ bid to place missiles in Cuba and had taken the opportunity to attack India (see below China, India, and Pakistan), and the precipitous Soviet retreat prompted Chinese charges of “capitulationism.” The Chinese nuclear program proceeded apace, with the People’s Republic exploding its first atomic device in 1964. Never again would the Soviet leadership hope to control the foreign policy of the other Communist giant.

Renewed U.S.–Soviet cooperation

U.S.–Soviet relations, by contrast, markedly improved after the sobering visit to the brink of war. Hopes for a comprehensive nuclear test-ban treaty ran afoul of the U.S.S.R.’s customary refusal to permit on-site inspection to monitor underground tests, but a partial Test-Ban Treaty was signed by the United States, Britain, and the U.S.S.R. on August 5, 1963, prohibiting nuclear explosions in the air, under the sea, and in outer space. The superpowers also established a direct communications link between Washington and Moscow for use in crisis situations. Other powers anxious to join the nuclear club, notably China and France, refused to adhere to the Test-Ban Treaty. Instead, the Chinese denounced Soviet collaboration with “the leader of world imperialism.” Mao resurrected all of China’s territorial claims against the Soviet Union dating from tsarist Russian imperialism and advocated partition of the Soviet empire. The Soviets, in turn, branded Mao with their most hateful current epithet: he was “another Stalin.”

President Kennedy was assassinated on November 22, 1963, and Khrushchev was removed from power by the Politburo in October 1964, a victim of his own failures in foreign policy and agriculture and of the Communist Party’s resistance to his attempted reforms. The bilateral effort to pursue arms control survived under President Johnson and under Leonid Brezhnev and Aleksey Kosygin. The Outer Space Treaty ratified in 1967 banned nuclear weapons and other weapons of mass destruction in the Earth’s orbit and on the Moon. A U.S.–Soviet draft Non-proliferation Treaty was also adopted by the UN in June 1968. (Once again, France, China, India, Pakistan, and Israel refused to sign.) None of the arms-control instruments of the 1960s, however, put a cap on the arms race or restrained the signatories from doing anything in the strategic area they had a desire to do anyway. The superpowers were able to modernize their arsenals through underground nuclear testing; outer space was an awkward and vulnerable place to deploy warheads in any case; and neither superpower had an interest in seeing nuclear weapons spread to more countries. Rather, American nuclear policy aimed, at least in the short run, at ensuring the continued stability of U.S.–Soviet deterrence, lately dubbed “mutual assured destruction.” Adopting the views of the strategist Bernard Brodie, McNamara concluded early on that the Soviets must eventually catch up and that a state of parity was the best that could be achieved in the nuclear age. Soon each side would be capable of obliterating the other in a retaliatory strike, even after a sneak attack. At that point, any attempt by either side to achieve an illusory superiority would only destabilize the balance and tempt one or the other into launching a first strike. Whether the Soviets ever shared this doctrine of deterrence is dubious. Marshal Sokolovsky’s volumes on military strategy in the 1960s, while granting that nuclear war would be an unprecedented disaster for all, still committed the U.S.S.R. to a war-winning capability.

China, meanwhile, succumbed to another series of Maoist actions that completed that country’s drift into chaos and isolation. In February 1966, Mao gave the nod to the young and fanatical Red Guards to make, by force, a Cultural Revolution. Violence swallowed up schools, factories, bureaucracies, cultural institutions, and everything that smacked of foreign or traditional Chinese influence. Countless victims suffered internal exile, public humiliation, forced “self-criticism,” or death, while attacks on foreign embassies and denunciations of the superpower “condominium” persuaded Americans and Soviets alike that the Chinese were, for the moment at least, the major threat to world peace.

By the late 1960s, therefore, relations between the United States and the Soviet Union underwent a marked thawing. At the same time, however, the Soviets and Americans alike had to acknowledge a growing lack of control over their once coherent Cold War camps.