The armed conflict fought in Vietnam from 1959 to 1975 began as a guerrilla campaign by the Vietcong in South Vietnam, backed by North Vietnam. It escalated in the 1960s into an international conflict as the United States backed South Vietnam, firstly with advisers, and then deploying over 500,000 combat troops by 1968. US forces withdrew in 1973; Saigon, the capital of South Vietnam, fell to the Communists in 1975. Geographical neighbours Laos and Cambodia were also drawn into the conflict.