Buddhism, the principal organized religion of Vietnam, was first introduced to Indochina in 111 B.C., when the Chinese conquered the Red River Delta. During the next thousand years, Buddhism fitted comfortably into the animist faith of ordinary people and became the dominant popular religion. During the imperial dynasties of the middle ages, Buddhism acquired a strong political base as well, and a Buddhist hierarchy saw to it that it became a state religion, complete with tax support and positions of influence in the imperial court. By the fifteenth century, Buddhism had lost some of its imperial influence to Confucianism and Taoism, but it retained its influence among common people. Not until the twentieth century did Vietnamese Buddhism enjoy a revival among intellectual elites and the upper class.

Buddhist doctrine revolved around the idea of successive lives for individuals. After suffering the challenges of life, individuals of merit would undergo successive lives through reincarnation. A cycle of birth, death, and rebirth governed individual life until one reached the state of nirvana, a condition of eternal peace. Only as an individual transcended worldly needs could he or she approach nirvana. In Vietnam, Mahayana Buddhism became the dominant religious strain. Its comfortable approach to saints and supernatural beings made it fit nicely into Vietnamese animism, and its ritual and imagery pleased the peasants. Mahayana Buddhism also viewed Gautama Buddha, founder of the religion, not as the one, single Buddha but one of a number of great teachers and leaders.

During the reign of Ngo Dinh Diem, Roman Catholicism assumed special prominence in Vietnamese affairs. Catholics filled key posts in the civil service, police, and military, and Roman Catholicism increased in size because of the mass influx of Catholic refugees from North Vietnam and increased conversion rates by South Vietnamese who saw the religion as an opportunity for economic advancement and political influence. The fact that Diem harshly repressed all political opposition, including the disorganized Buddhist leaders, contributed to a powerful resurgence of Buddhist influence. Buddhists began organizing in the 1950s in response to the pro-Catholic, anti-Buddhist posture of Diem. They formed the General Buddhist Association in 1955 in an attempt to provide some centralized direction to Buddhist political influence; and after the assassination of Diem in 1963, they filled a political vacuum in South Vietnam. The Buddhist Reunification Congress met at Xa Loi Pagoda in Saigon in December 1963; and the next month. they organized the United Buddhist Church of Vietnam, which soon won the support of most Buddhist sects in South Vietnam.

Buddhists in Hue and Da Nang, led by Thich Tri Quang, were generally quite militant in their opposition to the Saigon government, while Buddhists in Saigon, led by Thich Thien Khiet and Thich Tam Chau, were more circumspect and conservative. In South Vietnam, the Buddhists condemned communism as atheistic, denounced military governments in all forms, and rejected any political influence Roman Catholicism seemed to have. Their opposition to General Nguyen Khanh's military government brought his downfall in August 1964, and they were similarly r esponsible for the collapse of Tran Van Huong's government in January 1965. In April, 1966, General Nguyen Cao Ky transferred power to an elected body primarily because of Buddhist influence. In May 1966, the Buddhists organized military demonstrations throughout the country, complete with marches and the widely publicized self-immolations and General Nguyen Cao Ky sent soldiers out to crush the demonstrations. Buddhist political influence would never be the same again, primarily because American military power was firmly behind the government of Nguyen Van Thieu and Nguyen Cao Ky. Although Buddhists represented 80 percent of the South Vietnamese population, their political influence was all but eclipsed by the crushing defeat of 1966.