Vietnam War: A coup d'état replaces Dương Văn Minh with General Nguyễn Khánh as President of South Vietnam. A new constitution is established with aid from the U.S. Embassy.

The Vietnam War was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam and South Vietnam and their allies. North Vietnam was supported by the Soviet Union and China, while South Vietnam was supported by the United States and other anti-communist nations. The conflict was the second of the Indochina wars and a proxy war of the Cold War between the Soviet Union and US. The Vietnam War was one of the postcolonial wars of national liberation, a theater in the Cold War, and a civil war, with civil warfare a defining feature from the outset. Direct US military involvement escalated from 1965 until its withdrawal in 1973. The fighting spilled into the Laotian and Cambodian Civil Wars, which ended with all three countries becoming communist in 1975.

A coup d'état, or simply a coup, is typically an illegal and overt attempt by a military organization or other government elites to unseat an incumbent leadership. A self-coup is said to take place when a leader, having come to power through legal means, tries to stay in power through illegal means.

Dương Văn Minh was a South Vietnamese politician and military officer who was a senior general in the Army of the Republic of Vietnam (ARVN) and a politician during the presidency of Ngô Đình Diệm. In 1963, he became chief of a military junta after leading a coup in which Diệm was assassinated. Minh lasted only three months before being toppled by Nguyễn Khánh, but assumed power again as the fourth and last president of South Vietnam in April 1975, two days before surrendering to North Vietnamese forces. He earned his nickname "Big Minh", because he was approximately 1.83 m (6 ft) tall and weighed 90 kg (198 lb).

Nguyễn Khánh was a South Vietnamese military dictator and Army of the Republic of Vietnam general who served in various capacities as head of state and prime minister of South Vietnam while at the head of a military junta from January 1964 until February 1965. He was involved in or against many coup attempts, failed and successful, from 1960 until his defeat and exile from South Vietnam in 1965. Khánh lived out his later years with his family in exile in the United States. He died in 2013 in San Jose, California, at age 85.