The Republic of Vietnam was proclaimed on 26 October 1955, with Ngô Đình Diệm as its first president, after having briefly served as premier under Emperor Bảo Đại who was exiled. Its sovereignty was recognized by the United States and 87 other nations. It had membership in several special committees of the United Nations, but its application for full membership was rejected in 1957 because of a Soviet veto (neither South nor North Vietnam were members of the UN during the Vietnam War, but the united Vietnam became a member state in 1977). South Vietnam's origins can be traced to the French colony of Cochinchina, which consisted of the southern third of Vietnam which was Cochinchina [Nam Kỳ], a subdivision of French Indochina, and the southern half of Central Vietnam or Annam [Trung Kỳ] which was a French protectorate. After the Second World War, the anti-Japanese Việt Minh guerrilla forces, led by Ho Chi Minh, proclaimed the establishment of a Democratic Republic of Vietnam in Hanoi in September 1945, issuing a Declaration of Independence modeled on the U.S. one from 1776.
In 1949, anti-communist Vietnamese politicians formed a rival government in Saigon led by former emperorBảo Đại. Bảo Đại was deposed by Prime Minister Ngô Đình Diệm in 1955, who proclaimed himself president after a referendum. Diệm was killed in a military coup led by general Dương Văn Minh in 1963, and a series of short-lived military governments followed. General Nguyễn Văn Thiệu then led the country after a U.S.-encouraged civilian presidential election from 1967 until 1975. The beginnings of the Vietnam War occurred in 1955 with an uprising by the newly organized National Liberation Front for South Vietnam (Việt Cộng), armed and supported by the northern Democratic Republic of Vietnam, with other assistance rendered by the Soviet Union and its Warsaw Pact communist satellites, along with neighboring People's Republic of China and North Korea. Larger escalation of the insurgency occurred in 1965 with the landing of United States regular forces of Marines, followed by Army units to supplement the cadre of military advisors guiding ARVN (Army of the Republic of Vietnam) southern forces. A regular bombing campaign over North Vietnam was conducted by offshore U.S. Navy airplanes, warships, and aircraft carriers joined by Air Force squadrons through 1966 and 1967. Fighting peaked up to that point during the Tet Offensive of February 1968, when there were over a million South Vietnamese soldiers and 500,000 U.S. soldiers in South Vietnam. Later on the war turned into a more conventional fight as the balance of power became equalized. An even larger, armored invasion commenced during the Easter Offensive following U.S. ground-forces withdrawal, and had nearly overran some major northern cities until beaten back.
The official name of the South Vietnamese state was Việt Nam Cộng hòa (Republic of Vietnam) and the French name was referred to as République du Viêt Nam. The North was known as the "Democratic Republic of Vietnam".
Việt Nam (Vietnamese pronunciation: [vjə̀tnam]) was the name adopted by Emperor Gia Long in 1804. It is a variation of "Nam Việt" (南越, Southern Việt), a name used in ancient times. In 1839, Emperor Minh Mạng renamed the country Đại Nam ("Great South"). In 1945, the nation's official name was changed back to "Vietnam". The name is also sometimes rendered as "Viet Nam" in English. The term "South Vietnam" became common usage in 1954, when the Geneva Conference provisionally partitioned Vietnam into communist and non-communist parts.
Other names of this state were commonly used during its existence such as Free Vietnam and the Government of Viet Nam (GVN).