Laos and Cambodia were both drawn into the Vietnam War because of atrocities the people of these two countries suffered under the hands of North Vietnam. South Vietnam and other countries were trying to keep the North Vietnamese army from spreading Communism in these countries.
China, Russia, and later Cuba.
America's reaction to the war, was largely due to the draft, protests and riots.
During the Vietnam War, all combatants (including North Vietnam) used draftees except for the New Zealanders, they sent volunteers to South Vietnam.
Vietnam has never had a civil war. The closest you could get would be the Vietnam War, which was fought between the separate although related countries of North and South Vietnam (along with the allies of each side).
WWII, Korean War, then Vietnam War
After the war, there was a reunification of Vietnam. So the answer is "One country".
Vietnam , America , and Russia
WWII, Korean War, then Vietnam War
the tet offensive
The Vietnam War was part of the cold war. The cold war was between governments (Nations/Countries).
North Vietnam/VC vs allies
North Vietnam won them.
Draft protests and riots.
All countries and all people's will have differing views on all things. For this particular question, Australia's "views" and "involvement" mirrored Americas.
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 Soviet Union (USSR) supplied North Vietnam, and the US fought for South Vietnam.