The Republic of Vietnam, commonly known as South Vietnam, was a state in Southeast Asia that existed from 1955 until 1975. It was established after the division of Vietnam into two parts following the First Indochina War. The capital was Saigon, and the government was led by President Ngô Đình Diệm until his assassination in 1963. The Republic of Vietnam was supported by the United States and other anti-communist nations during the Vietnam War, which aimed to prevent the spread of communism from the northern part of the country, known as North Vietnam. The conflict ended with the fall of Saigon in 1975, leading to the reunification of Vietnam under communist control.