What happened to Vietnam in relation to the Cold War?
While the war was between communist North Vietnam and the government of South Vietnam it was also a platform for other governments to advance their own agendas. North Vietnam had the Soviet Union (and other communist nations) supporting them, while South Vietnam had the United States and their allies for support.
The Soviet Union supplied North Vietnam with weapons, vehicles, and medical aid. As well as stationing a few thousand troops in North Vietnam during the war. The government of South Vietnam requested the help of the "free world" to ensure their freedom. The United States and her allies responded by engaging in one of the most controversial wars in recent history.
So the Vietnam war became a proxy for both superpowers during the Cold War. The Soviet Union used Vietnam as a means to weaken the U.S. without being personally responsible for it. The Soviets equipped the Viet Cong with the means to keep up an effective campaign of hit-and-run type attacks and due to the distance, terrain and social climate of the times the U.S. forces weren't particularly well equipped to handle the conflict.
hope this helped.