In 111 BC ancestors of the present-day Vietnamese who inhabited part of what is now forces of China's Han dynasty conquered southern China and northern Vietnam. Chinese rule lasted more than 1000 years (until 939 AD) when the Vietnamese ousted their conquerors and began a southward expansion that, by the mid-18th century, reached the Gulf of Siam. Despite their military achievements the Vietnamese continued to suffer from internal political divisions. Throughout most of the 17th and 18th centuries, contending families in the north and south struggled to control the powerless kings of the Le dynasty.
Vietnam was reunited following a devastating civil war in the 18th century but soon fell prey to the expansion of European colonialism. The French conquest of Vietnam began in 1858 with an attack on what is now the city of Danang.
FIiercely nationalistic, the Vietnamese never truly accepted the imposition of French rule. By 1930, the Vietnamese Nationalist Party had staged the first significant armed uprising against the French, but its virtual destruction in the ensuing French repression left the leadership of the anti-colonial movement to those more adept at underground organization and survival - the communists.
A prolonged three-way struggle ensued among the Vietnamese communists (led by Ho Chi Minh), the French, and the Vietnamese nationalists (nominally led by Emperor Bao Dai). Ho Chi Minh's Viet Minh forces fought a highly successful guerrilla campaign and eventually controlled much of rural Vietnam. The French military disaster at Dien Bien Phu in May 1954 and the conference at Geneva, where France signed the Agreement on the Cessation of Hostilities in Vietnam on July 20, 1954, marked the end of the eight-year war and French colonial rule in Indochina.
By 1963 the Vietnamese communists had made significant progress in building a strong network of supporters in South Vietnam. Nevertheless, in 1964 Hanoi decided that the Viet Cong (VC) cadres and their supporters were not sufficient to take advantage of the political confusion following the overthrow of Diem in November 1963. Hanoi ordered regular troops of the North Vietnamese army (People's Army of Vietnam - PAVN) into South Vietnam, first as 'fillers' in VC units, then in regular formations. The first regimental units were dispatched in the autumn of 1964. By 1968, PAVN forces were enduring most combat on the communist side.
In December 1961 President Diem requested assistance from the United States. President Kennedy sent US military advisers to South Vietnam to help the government deal with the instability that plagued the southern part of Vietnam. By the spring of 1969 the United States had reached its greatest troop strength - 543,000 - in Vietnam.
While the United States withdrew from ground combat by 1971, it still provided air and sea support to the South Vietnamese until the signing of the cease-fire agreements. The peace agreement was concluded on January 27, 1973. At the beginning of 1975, the North Vietnamese began a major offensive in the South that succeeded in breaking through the central highlands defenses. After taking over provincial capitals in that area, a combination of forces from the demilitarized zone area and the highlands led to the withdrawal of South Vietnamese forces.
For the first few months after the war, separate governments were maintained in the northern and southern parts of the country. However, in mid-November 1975, the decision to reunify the country was announced, despite the vast social and economic differences remaining between the two sections. The assembly ratified the reunification of the country and on July 2 renamed it the Socialist Republic of Vietnam (SRV). It also appointed a committee to draft a new constitution for the entire country.