information:highlighting, quality:correction
South Vietnam, officially the Republic of Vietnam, was a country in Southeast Asia that existed from 1955 to 1975, the period when the southern portion of Vietnam was a member of the Western Bloc during part of the Cold War after the 1954 division of Vietnam. It first received international recognition in 1949 as the State of Vietnam within the French Union, with its capital at Saigon, before becoming a republic in 1955. South Vietnam was bordered by North Vietnam to the north, Laos to the northwest, Cambodia to the southwest, and Thailand across the Gulf of Thailand to the southwest. Its sovereignty was recognized by the United States and 87 other nations, though it failed to gain admission into the United Nations as a result of a Soviet veto in 1957. It was succeeded by the Republic of South Vietnam in 1975. In 1976, the Republic of South Vietnam and North Vietnam merged to form the Socialist Republic of Vietnam. The end of the Second World War saw anti-Japanese Việt Minh guerrilla forces, led by communist fighter Ho Chi Minh, proclaiming the establishment of the Democratic Republic of Vietnam in Hanoi in September 1945. In 1949, during the First Indochina War, the French formed the State of Vietnam, a rival government of anti-communist Vietnamese politicians in Saigon, led by former emperor Bảo Đại. A 1955 referendum on the state's future form of government was widely marred by electoral fraud and resulted in the deposal of Bảo Đại by Prime Minister Ngô Đình Diệm, who proclaimed himself president of the new republic on 26 October 1955. After the 1954 Geneva Conference, it abandoned its claims to the northern, Việt Minh-controlled part of the country, and established its sovereignty over the southern half of Vietnam consisting of Cochinchina, a former French colony; and parts of Annam, a former French protectorate. Diệm was killed in a CIA-backed 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 US-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, armed and supported by North Vietnam, with backing mainly from China and the Soviet Union. Larger escalation of the insurgency occurred in 1965 with American intervention and the introduction of regular forces of Marines, followed by Army units to supplement the cadre of military advisors guiding the Southern armed forces. A regular bombing campaign over North Vietnam was conducted by offshore US 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 US soldiers in South Vietnam. What started as a guerrilla war eventually turned into a more conventional fight as the balance of power became equalized. An even larger, armored invasion from the North commenced during the Easter Offensive following US ground-forces withdrawal, and had nearly overrun some major southern cities until being beaten back. Despite a truce agreement under the Paris Peace Accords, concluded in January 1973 after five years of on-and-off negotiations, fighting continued almost immediately afterwards. The regular North Vietnamese army and Việt-Cộng auxiliaries launched a major second combined-arms conventional invasion in 1975. Communist forces overran Saigon on 30 April 1975, marking the end of the Republic of Vietnam. On 2 July 1976, the North Vietnam-controlled Republic of South Vietnam and the Democratic Republic of Vietnam merged to form the Socialist Republic of Vietnam.