Despite the aggressive U.S. militarism in Southeast Asia, and a brutal Soviet invasion of Czechoslovakia in 1968, a new thaw in East-West relations emerged in the 1960s and 1970s. Détente (relaxation of tensions) emerged as part of the cyclical pattern of Cold War history in which periods of relative calm followed periods of bitter great-power conflict. Kennedy and Khrushchev started the process in the wake of the missile crisis, but both were removed from the scene with Kennedy's assassination in Dallas and Khrushchev's ouster in a 1964 Kremlin power shift. The new, hard-line regime of Leonid Brezhnev aggressively pursued Soviet aims, including sending the Red Army into Czechoslovakia to repress the "Prague Spring." Although the Czechs had not rejected the Warsaw Pact alliance with the Soviet Union, the Brezhnev Doctrine proclaimed that none of the East European states would be allowed to vacate the communist camp.
Preoccupied with his foreign policy debacle in Vietnam, Lyndon Johnson made little progress toward détente, but his successor, Nixon, was keenly interested in improved East-West relations. Nixon's support for détente was ironic, since he had made his reputation in politics as a fervent anticommunist, yet he would achieve a breakthrough in the Cold War. The impetus for détente, however, actually came from European leaders Charles de Gaulle, president of France, and Willy Brandt, the West German chancellor. Bitterly opposed to the U.S. war in the former French colony of Indochina, De Gaulle excoriated U.S. foreign policy, withdrew France from NATO's integrated military command, and met with Brezhnev in Moscow in 1966. Brandt, a former mayor of West Berlin, pursued a diplomacy of Ostpolitik (Eastern policy), improving relations with neighboring East Germany.
Nixon and Henry A. Kissinger, a refugee from Nazi Germany and a former Harvard professor turned national security adviser, pursued détente in part to prevent the Europeans from undermining Washington's leadership. Nixon and Kissinger also hoped to use improved relations to gain the assistance of Moscow and Beijing in bringing an end to the Vietnam War without the United States suffering a humiliating defeat. Nixon and Kissinger exploited the Sino-Soviet rift with a "triangular diplomacy" that sought to play off the great communist powers against one another to the betterment of U.S. national interests. After Kissinger traveled secretly to Beijing for talks in 1969, the momentum toward rapprochement (reconciliation) was irreversible. During a dramatic state visit in 1971, Nixon clinked cocktail glasses with Mao Zedong in Beijing and posed for photographers atop the Great Wall of China. The next year the two powers issued the Shanghai Communique, a joint statement that China and the United States would strive to improve their relations and to contain "hegemony," a euphemism for the Soviet Union.
The dramatic "Nixinger" summit diplomacy with the onetime archenemy "Red" China wowed the American public and created anxiety in Moscow. The Kremlin warned the Americans against playing the "China card" but also received Nixon in Moscow in 1972 despite the American mining of Haiphong Harbor in North Vietnam, where Soviet supply ships regularly anchored. The high point of the U.S.–Soviet détente was the signing of the 1972 Strategic Arms Limitation Agreement, known as SALT I. The treaty established ceilings on offensive missiles and sharply limited destabilizing defensive weapons systems, but it was more important as a political vehicle for improved relations than for its actual achievements in limiting the weapons of mass destruction. Nixon and Kissinger failed completely in their quest to go through China and the Soviets to prevail upon North Vietnam to accept an independent South Vietnam, which instead fell in April 1975.
The momentum of détente began to wane in the mid-1970s. Nixon, its chief architect, met his political demise in the Watergate scandal. With the Soviet Union maintaining its hegemony over Eastern Europe, sponsoring revolutionary movements in the Third World, and denying human rights to many of its own citizens, American critics began to equate détente with appeasement. In the southwest African nation of Angola, the two superpowers backed competing forces in a raging civil war. Cuban troops, viewed as Soviet "proxies," fought in behalf of leftist rebels in Angola while the United States and China supported the opposition. A Cold War battle also emerged in Ethiopia and throughout the horn of Africa. Soviet and Cuban influence was confined mainly to those two countries, as U.S. trade and diplomacy proved advantageous in several other key African states.
Critics of détente advocated "linkage"— linking trade, arms control, and improved relations with Soviet behavior in world affairs and in the regime's human rights policies. The Soviets bitterly resented this approach and any effort to influence their internal affairs. They had left themselves vulnerable to such criticism, however, not only by denying freedom of intellectual and religious expression in Russia but by violating pledges to respect human rights embodied in the 1975 Helsinki Accords. Under this agreement, the United States, Soviet Union, and governments throughout Europe recognized current borders as permanent, thus in effect renouncing the old U.S. Cold War depiction of Eastern Europe as a set of "captive nations."
Jimmy Carter, elected president in 1976, advocated arms control but made human rights the centerpiece of his diplomacy and criticized the Soviets for their violations. U.S. relations with China continued to improve, however, a process that culminated in 1979 with formal recognition of Beijing at the expense of the longtime U.S. ally on Taiwan. The Japanese, too, expressed dismay at not being consulted about the dramatic shift in U.S. East Asian policy. Détente deteriorated under Carter, who adopted conflicting policies that reflected the conflicting advice he received from Secretary of State Cyrus Vance, an advocate of détente, and national security adviser Zbigniew Brzezinski, a Polish emigré who adopted a harder line toward the Soviets. Carter himself allowed the SALT process to break down. Although a SALT II treaty was negotiated, Carter never took it before the U.S. Senate, where it faced rejection.
Two climactic events in 1979 destroyed détente and ensured Carter's defeat in the 1980 presidential election. First, in November a militant fundamentalist regime in Iran took over the U.S. embassy in Tehran, holding fifty-three Americans hostage. Carter began painstaking negotiations aimed at securing their release, which would not come for more than year. Meanwhile, the United States appeared helpless as Iranian radicals burned the U.S. flag and shouted "Death to Carter" in daily rituals outside the embassy. In December the Soviet Union launched an invasion of neighboring Afghanistan, where the pro-Soviet government in Kabul had come under siege. The Soviet assault seemed to confirm critics' charges that détente had been a form of appeasement. Carter declared that Brezhnev had lied to him and instituted a variety of sanctions, including a U.S. boycott of the 1980 Olympic games in Moscow.