Who were the bad guys in the vietnam war?

Depends upon where you are from. If you're from the communist block nations (or former communist block countries) then the enemy (bad guys) were the US & allies. If you're from the former free world nations (or "current" free world nations...Europe, America, Australia, etc.) then the enemy (bad guys) were the NVA & VC (and suppliers).

NVA=North Viet Army

VC=Viet Cong

USSR/Red China-Suppliers of tanks, jets, missiles, small arms, medical supplies, artillery, shells, land mines, etc.