 From 1965 to 1973, U.S. troops fought at the request of the governments of South Vietnam, Laos, and Cambodia during the Vietnam War against the military of North Vietnam and against Viet Cong, Pathet Lao, and Khmer Rouge insurgents.President Lyndon Johnson escalated U.S. involvement following the Gulf of Tonkin Resolution.North Vietnam invaded Laos in 1959, and used 30,000 men to build invasion routes through Laos and Cambodia.