The South part.
When France left Vietnam in 1954 part of the country was controlled by the communists, and part was democratically controlled. The Communist controlled are became North Vietnam, and the Democratic area became South Vietnam.
During the Viet War North Vietnam was a communist nation; the Republic of South Vietnam, which no longer exists, was a free democratic nation. After the war ended in 1975 both N & S Vietnam became one communist country (because North Vietnam won the war, they conquered the Republic of South Vietnam).
They controlled North Vietnam, the Ho Chi Minh Trail, and probably controlled the their ally, the VC.
North
When NVA Tank #844 crashed thru the South Vietnamese Capital's front gates in April 1975: South Vietnam became part of communist North Vietnam.
The south, because that part of Vietnam was non-communist
The Northern Communist part of Vietnam came out victorious, they declared Independance and even to this day they could still be partly Communist
Vietnam is part of the communist world.
Part of the cold war. To thwart communist expansionism which was then known as part of the "Domino Theory" ; see related link .
Part of the cold war. Stopping communist aggression.
The five current communist countries are:China(1949)Cuba(1961)North Korea(1948)Vietnam(1976)Laos(1975)
The Vietnam War was part of the cold war. To prevent Communist North Vietnam from taking over the Republic of South Vietnam.