The Vietnam War was a long, costly and divisive conflict that pitted the communist government of North Vietnam against South Vietnam, a more democratic area and a principal ally of the United States. Active U.S. involvement begin in 1954. The conflict was intensified by the ongoing Cold War between the United States and the Soviet Union.
In 1961, working under the “domino theory,” which held that if one Southeast Asian country fell to communism, many other countries would follow, President Kennedy increased U.S. aid, though he stopped short of committing to a large-scale military intervention. It wasn't until 1964, when following the assassination of Kennedy, Lyndon B. Johnson increased U.S. military and economic support. The torpedoing of two U.S. destroyers resulted in retaliatory bombing of military targets in North Vietnam and neighboring Loas. Between 1965 and 1966, amid growing anti-war sentiment, Johnson had authorized the dispatch of 200,000 troops.
Protests across the country in the latter half of the 1960s were part of organized opposition against U.S. military activities in Southeast Asia as well as the military draft. Opposition to the war in the United States bitterly divided Americans, even after President Richard Nixon signed the Paris Peace Accords and ordered the withdrawal of U.S. forces in 1973. Communist forces ended the war by seizing control of South Vietnam in 1975, and the country was unified as the Socialist Republic of Vietnam the following year. More than 3 million people (including over 58,000 Americans) were killed in the Vietnam War, and more than half of the dead were Vietnamese civilians.