Nobody knows.
Too bad.
The Soviet Union (USSR) supplied North Vietnam, and the US fought for South Vietnam.
The fight against the spread of Communism.
The countries that were actually "physically" involved, and were bombed or had US aircraft crash into them, whether they were "officially" in the war or not, were: Lao's, Cambodia, North Vietnam and South Vietnam.
The United States did get involved in the Vietnam war because of communism in Vietnam.
North Vietnam and South Vietnam. Also, to name just a few: the USA, China, Russia, South Korea, Australia, France, and England. A great many countries fought in the Vietnam War from 1945 to 1975.
korea, united states, ussr, vietnam, and germany?
The north won the war. No need for agreements.
Primary combatants were US & North Vietnam; especially the air war over the North.
The UK was not involved in the Vietnam war - it was the USA!
They weren't.
No, only a couple of Asian countries contributed to WW1 but Vietnam wasn't one of them. The only countries that did participate were colonies of the European countries which were involved.
Vietnam war