(1955–75) Protracted effort by South Vietnam and the U.S. to prevent North and South Vietnam from being united under communist leadership. After the First Indochina War, Vietnam was partitioned to separate the warring parties until free elections could be held in 1956. Ho Chi Minh's popular Viet Minh party from the north was expected to win the elections, which the leader in the south, Ngo Dinh Diem, refused to hold. In the war that ensued, fighters trained in the north (the Viet Cong) fought a guerrilla war against U.S.-supported South Vietnamese forces; North Vietnamese forces later joined the fighting. At the height of U.S. involvement, there were more than half a million U.S. military personnel in Vietnam. The Tet Offensive of 1968, in which the Viet Cong and North Vietnamese attacked 36 major South Vietnamese cities and towns, marked a turning point in the war. Many in the U.S. had come to oppose the war on moral and practical grounds, and Pres. Lyndon B. Johnson decided to shift to a policy of “de-escalation.” Peace talks were begun in Paris. Between 1969 and 1973 U.S. troops were withdrawn from Vietnam, but the war was expanded to Cambodia and Laos in 1970. Peace talks, which had reached a stalemate in 1971, started again in 1973, producing a cease-fire agreement. Fighting continued, and there were numerous truce violations. In 1975 the North Vietnamese launched a full-scale invasion of the south. The south surrendered later that year, and in 1976 the country was reunited as the Socialist Republic of Vietnam. More than 2,000,000 people (including 58,000 Americans) died over the course of the war, about half of them civilians.
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A distinct Vietnamese group began to emerge circa 200 BC in the independent kingdom of Nam Viet, which was later annexed to China in the 1st century BC. The Vietnamese were under continuous Chinese control until the 10th century AD. The southern region was gradually overrun by Vietnamese from the north in the late 15th century. The area was divided into northern and southern dynasties in the early 17th century, and in 1802 these two parts were unified under a single dynasty. Following several years of attempted French colonial expansion in the region, the French captured Saigon (now Ho Chi Minh City) in 1859 and later the rest of the area, controlling it until World War II (see French Indochina). The Japanese occupied Vietnam in 1940–45 and allowed the Vietnamese to declare independence at the end of the war, a move the French opposed. The First Indochina War ensued and lasted until French forces with U.S. financial backing were defeated by the Vietnamese at Dien Bien Phu in 1954; evacuation of French troops followed. After an international conference at Geneva (April–July 1954), Vietnam was partitioned along latitude 17° N, with the northern part under the communist leadership of Ho Chi Minh and the southern part under the U.S.-supported former emperor Bao Dai; the partition was to be temporary, but the reunification elections scheduled for 1956 were never held. An independent South Vietnam (Republic of Vietnam) was declared, while the communists established North Vietnam (Democratic Republic of Vietnam). The activities of North Vietnamese guerrillas and procommunist rebels in South Vietnam led to U.S. intervention and the Vietnam War. A cease-fire agreement was signed in 1973 and U.S. troops withdrawn, but the civil war soon resumed; in 1975 North Vietnam invaded South Vietnam, and the South Vietnamese government collapsed. In 1976 the two Vietnams were united as the Socialist Republic of Vietnam. From the mid-1980s the government enacted a series of economic reforms and began to open up to Asian and Western nations. In 1995 the U.S. officially normalized relations with Vietnam.
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Between 1953 and 1956, the DRVN government instituted various agrarian reforms, including land redistribution. Large landowners were publicly denounced as landlords (địa chủ), and their land distributed to poor and middle peasants.
A literary movement called Nhân văn-Giai phẩm (from the names of the two magazines which started the movement) attempted to encourage the democratization of the country and the free expression of thought.
In December 1960, the Vietnam Workers' Party co-initiated and began working within the National Liberation Front of South Vietnam (referred to by the South as the Việt Cộng) which was organized to support reunification and oppose the government of South Vietnam. After August 1964, this was expanded to armed opposition to the military presence and operations of the United States in the southern areas of Vietnam. From at least 1965 onwards, both China and the Soviet Union provided aid to North Vietnam in support of its military activities; known in the West as the Vietnam War and in Vietnam as the American War.
In June 1969, in the South, the NLF formed a Provisional Revolutionary Government in order to present an organized alternative government to the international community.
With the fall of Saigon to National Liberation Front and regular North Vietnamese armed forces on April 30, 1975, political authority within South Vietnam was assumed by the Provisional Revolutionary Government of the Republic of South Vietnam. This government merged with Democratic Republic of Vietnam on July 2, 1976, to form a single nation officially called the Democratic Republic of Vietnam (Cộng Hoà Xã Hội Chủ Nghĩa Việt Nam), or more commonly known as Việt Nam.