From Wikipedia

Cold War: Vietnam (1954-1968)

U.S. President Lyndon B. Johnson landed 42,000 troops in the Dominican Republic in 1965 to prevent the emergence of "another Fidel Castro." More notable in 1965, however, was U.S. intervention in Southeast Asia. In 1965 Johnson stationed 22,000 troops in South Vietnam to prop up the faltering anticommunist regime. The South Vietnamese government had long been allied with the United States. The North Vietnamese under Ho Chi Minh were backed by the Soviet Union and China. North Vietnam, in turn, supported the National Liberation Front, which drew its ranks from the South Vietnamese working class and peasantry. Seeking to contain Communist expansion, Johnson increased the number of troops to 575,000 in 1968.

Although neither the Soviet Union nor China intervened directly in the conflict, they did supply large amounts of aid and material to the North and supported them diplomatically.

While the early years of the war had significant U.S. casualties, the administration assured the public that the war was winnable and would in the near future result in a U.S. victory. The U.S. public's faith in "the light at the end of the tunnel" was shattered on January 30, 1968, when the NLF mounted the Tet Offensive in South Vietnam. Although neither of these offensives accomplished any military objectives, the surprising capacity of an enemy to even launch such an offensive convinced many in the U.S. that victory was impossible.

A vocal and growing peace movement centered on college campuses became a prominent feature as the counter culture of the 1960s adopted a vocal anti-war position. Especially unpopular was the draft that threatened to send young men to fight in the jungles of Southeast Asia.

Elected in 1968, U.S. President Richard M. Nixon began a policy of slow disengagement from the war. The goal was to gradually build up the South Vietnamese Army so that it could fight the war on its own. This policy became the cornerstone of the so-called "Nixon Doctrine." As applied to Vietnam, the doctrine was called "Vietnamization." The goal of Vietnamization was to enable the South Vietnamese army to increasingly hold its own against the NLF and the North Vietnamese Army.

The morality of U.S. conduct of the war continued to be an issue under the Nixon presidency. In 1969, it came to light that Lt. William Calley, a platoon leader in Vietnam, had led a massacre of Vietnamese civilians a year earlier. In 1970, Nixon ordered secret military incursions into Cambodia in order to destroy NLF sanctuaries bordering on South Vietnam.

The U.S. pulled its troops out of Vietnam in 1973, and the conflict finally ended in 1975 when the North Vietnamese took Saigon, now Ho Chi Minh City. Millions of Vietnamese died as a consequence of the Vietnam War. The lowest casualty estimates, based on the now-renounced North Vietnamese statements, are around 1.5 million Vietnamese killed. Vietnam released figures on April 3, 1995, that a total of one million Vietnamese combatants and four million civilians were killed in the war. The accuracy of these figures has generally not been challenged. The official estimate for U.S. death toll is about 58,000, with some missing and presumed dead. Millions of Vietnamese fled after the war ended. After the war, thousands of Vietnamese were rounded up into "re-education" camps. Since the mid-1980s, Vietnam has followed a path of economic liberalization similar to the Chinese model, and though still poor, over the past decade Vietnam has been one of the fastest growing economies in the world.