Universal Soldier appeared on It's My Way!, Buffy St Marie's first album, released by Vanguard Records in April 1964. It must have been an early - perhaps the very first - song to have been directly inspired by US participation in the Vietnam war. “I had been traveling from Mexico to Toronto and had a layover in San Francisco,” recalls Sainte-Marie. “In the middle of the night a group of medics came into the airport wheeling wounded soldiers and we got to talking. I asked one of them if there really was a war in Vietnam because the politicians at home were saying there wasn’t one. The medics assured me there was indeed a huge war going on. I started writing the song in the airport and on the plane, and I finished it in the basement of the Purple Onion in Toronto.”

Timeline; By 1964, 23,000 US advisors were stationed in South Vietnam. In the Gulf of Tonkin incident in August, a U.S. destroyer was alleged to have clashed with North Vietnamese fast attack craft. Shortly before midnight on August 4, Johnson interrupted national television to make an announcement in which he described an attack by North Vietnamese vessels on two U.S. Navy warships, Maddox and Turner Joy, and requested authority to undertake a military response. The U.S. Congress passed the Gulf of Tonkin Resolution and gave President Lyndon B. Johnson broad authority to increase American military presence in Vietnam. Johnson ordered the deployment of combat units for the first time and increased troop levels to 184,000. On 8 March 1965, two battalions of U.S. Marines waded ashore on the beaches at Danang. Those 3,500 soldiers were the first combat troops the United States had dispatched to South Vietnam to support the Saigon government. Thanks to Wikipedia.