The involvement of the United States in the Vietnam War began in the 1950s and greatly escalated in 1965 until its withdrawal in 1973. The U.S. military presence in Vietnam peaked in April 1969, with 543,000 military personnel stationed in the country. By the end of the U.S. involvement, more than 3.1 million Americans had been stationed in Vietnam, and 58,279 had been killed.
After World War II ended in 1945, President Harry S. Truman declared his doctrine of "containment" of communism in 1947 at the start of the Cold War. U.S. involvement in Vietnam began in 1950, with Truman sending military advisors to assist the French Union against Viet Minh rebels in the First Indochina War. The French withdrew in 1954, leaving North Vietnam in control of the country's northern half. President Dwight D. Eisenhower ordered covert CIA activities in South Vietnam. Opposition to the regime of Ngo Dinh Diem in South Vietnam was quashed with U.S. help, but from 1957 insurgents known as the Viet Cong launched a campaign against the state. North Vietnam supported the Viet Cong, which began fighting the South Vietnamese army. President John F. Kennedy, who subscribed to the "domino theory" that communism would spread to other countries if Vietnam fell, expanded U.S. aid to South Vietnam, increasing the number of advisors from 900 to 16,300, but this failed to produce results. In 1963, Diem was deposed and killed in a military coup tacitly approved by the U.S. North Vietnam began sending detachments of its own army, armed with Soviet and Chinese weapons, to assist the Viet Cong.