(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 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. {{link=Johnson, Lyndon Baines">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 Between 1969 and 1973 U.S. troops were withdrawn from Vietnam, but the war was expanded to Cambodia and Laos in 1970.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.