Though its interventions in Latin America were confounded by Castro’s Cuba and popular support for communist parties in other Central and South American countries, the United States continued to try to prevent the spread of communism, notably in Southeast Asia. Escalation in Vietnam In the summer of 1963, South Vietnamese generals, disgusted by the corruption of Ngo Dinh Diem’s regime and realizing his unpopularity was hampering their fight against North Vietnam and the Viet Cong, assassinated Diem and his brother Nhu. Though greeted with jubilation by most South Vietnamese, the killings did not lead to the creation of a democratic government. The country was afterward governed by a succession of leaders; none were effective or earned the loyalty of the population. All were maintained in power by the United States, which proved willing to support any politician promising to take a hard line against communism and continue the war against North Vietnam. The U.S. role in the Vietnam War intensified in 1964. In early August, U.S. ships stationed in the Gulf of Tonkin off the coast of North Vietnam reported they had come under attack. A crew member on duty believed he saw signs of a North Vietnamese torpedo strike on his sonar. Despite the fact that there was no other evidence to support the claim and the incident most likely did not take place, Congress passed the Gulf of Tonkin Resolution on August 7, 1964. The resolution gave President Lyndon Johnson permission to retaliate against North Vietnamese attacks and to act first to defend U.S. lives. The situation in Vietnam swiftly escalated. In 1965, Johnson committed U.S. ground forces and began the bombing of the North. Troops from other nations, including Australia, New Zealand, the Philippines, and South Korea, assisted in the fighting. The guerrilla war fought by the Viet Cong confounded U.S. troops, who came to see every Vietnamese peasant as a potential enemy. They relocated South Vietnamese farmers and burned their villages in an attempt to deny their opponents sources of support. In early 1968, however, a series of coordinated Viet Cong attacks that struck cities and military installations throughout South Vietnam during the lunar new year holiday of Tet called into question the success of the U.S. efforts. Although North Vietnamese officials later admitted the Viet Cong had suffered serious losses during the Tet Offensive, in the immediate aftermath it seemed as though the United States and South Vietnam were no closer to defeating North Vietnam than they had ever been. Many in the United States had already begun to question the military’s involvement in Vietnam and to call for the withdrawal of troops. Their opposition grew even more intense following the revelation in 1969 that U.S. troops had massacred unarmed peasants in the village of My Lai the year before. By the early 1970s, the United States was seeking a way to escape the situation in Vietnam. President Richard Nixon did not wish to simply withdraw, however. Instead, a peace agreement would have to be reached. North Vietnam had been reluctant to negotiate on U.S. terms, but damage to the relationship between two of its supporters, China and the Soviet Union, had threatened to isolate it and made it more amenable to seeking peace. The Sino-Soviet Split China and the Soviet Union had once been firm allies. The Soviet Union had supported the Chinese Communist Party since its founding and had signed the Treaty of Friendship, Alliance, and Mutual Assistance in 1950. It had given China both money and valuable technical assistance as the latter sought to build its industrial capacity. However, because Mao had greatly admired Stalin, he disapproved of Khrushchev’s 1956 denunciation of him. He also believed that as China’s leader since 1949, he had “seniority” over Khrushchev, in power only since 1953. In Mao’s eyes, he himself, not Khrushchev, should be the leader of world communism. The “Sino-Soviet split” widened when Khrushchev, fearing Mao’s insistence on attacking Taiwan might provoke war with the United States, refused to provide China with nuclear weapons. Khrushchev’s actions were representative of Mao’s chief criticism of the Soviet Union after the death of Stalin. The Soviets, Mao believed, had become too comfortable as leaders of the communist world and were no longer willing to risk confrontation with the United States or other imperialist powers if this would jeopardize their position. The USSR was doing too little, in the eyes of China, to support decolonization struggles in Africa and Asia and wars of independence. Indeed, far from being anti-imperialist, the Soviets had created their own empire in Europe. Other issues contributed to the rift. In the clash between India and China in 1962, for example, the USSR supported India; in 1969, Soviet and Chinese forces clashed in a dispute over their shared border. In the late 1960s, China cut back its financing of North Vietnam’s war against the South, and North Vietnam turned to the Soviet Union to fill the gap. The United States was eager to capitalize on the Sino-Soviet split in hopes of securing several advantages. In 1972 Nixon visited China, the first sitting U.S. president to do so, and met with Mao. This effort to improve U.S. relations with China threatened to isolate the Soviet Union, so in turn the Soviets agreed to hold a Moscow Summit meeting between Brezhnev and Nixon in May 1972. The United States then used the Soviet desire for closer relations to exert pressure on North Vietnam. In March 1972, after the North launched an offensive against the South, Nixon threatened to call off the Moscow Summit if the Soviets did not force North Vietnam to the peace table. In the end, the United States’ efforts to extricate itself from the war were successful. At the peace talks in Paris, North Vietnam and the United States agreed to the U.S. withdrawal from South Vietnam in 1973. The war continued until 1975, however, when North Vietnam defeated South Vietnam, and the country was reunified under a communist government. All told, the war had cost the lives of more than one million people. Genocide in Cambodia Although peace came to Vietnam in 1975, in neighboring Cambodia a nightmare was just beginning. Throughout much of the war in Vietnam, Cambodia had been neutral. In 1970, however, its ruler Prince Sihanouk was deposed by one of his generals, Lon Nol, who favored the United States. Sihanouk then allied himself with the Cambodian communist group, the Khmer Rouge. In 1975, after years of fighting, the Khmer Rouge overthrew the government of Lon Nol. Under the rule of Pol Pot, the Khmer Rouge leader and an admirer of Mao Zedong, Cambodia embarked on a program to rebuild itself as the perfect communist state. The Khmer Rouge seized private property and forced city dwellers to relocate to the countryside. The population was made to labor in work camps and on collective farms, and some died as a result of disease and starvation. Those who were unable to work were killed. The Khmer Rouge also carried out a deliberate campaign of extermination against professionals, intellectuals (which could mean anyone who wore glasses), Christians, Muslims, Buddhist monks, and people of Chinese, Thai, and Vietnamese ancestry. By the time the killing ended with the invasion of Cambodia by Vietnam in 1978, some three million people, approximately one-quarter of Cambodia’s population, had died. Although Southeast Asia remained mired in violence and turmoil, in the West there were new hopes for peace as the Cold War showed signs of thawing. At the 1972 Moscow Summit, the United States and the USSR signed the Strategic Arms Limitations Treaty (SALT), a mutual agreement to restrict the development of antiballistic missiles meant to destroy incoming warheads, thus rendering useless the defense strategy of mutually assured destruction. This marked the beginning of a period of détente, a relaxation of tensions between the United States and the Soviet Union that included trade agreements and additional arms-reduction talks. In 1975, the United States and the Soviet Union, along with Canada and all the countries of Europe, except for Albania, signed the Helsinki Accords. The United States and its allies pledged to respect the borders of Eastern Bloc countries and to refrain from intervening in their internal affairs. The Soviet Union promised to respect human rights.