The primary cause of the Vietnam War was the spreading of communism throughout Southeast Asia. North Vietnam, supported by China and the USSR, was controlled by the communist authorities who fought against South Vietnam supported by the United States.
In order to prevent the advancements of the North Vietnamese further into Southeast Asia forced the United States began the Vietnam War. The Gulf of Tonkin Incident was officially used by the U.S. government to justify the start of the military escalation. The United States attempted to avoid any direct involvement by providing support and assistance to South Vietnam. Nevertheless, the South Vietnamese were not able to address the threat posed by communism alone.