it is the french colonial empire
The Republic of South Vietnam (RVN) controlled themselves; hence the word "Republic." Note: The US/allies were invited to come (asked to come) by the RVN.
North Vietnam was controlled by communists.
Vietnam is a communist nation.
Vietnam. NOT France.
France. They left Vietnam after they were defeated by the Vietnamese at Dien Bien Phu. Lots of Vietnamese and French died during the battle.
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).
The nation of Vietnam came into existence in 1975 (on paper in 1976). So are you asking about that Vietnam or the Vietnam War? There was no nation called "Vietnam" during the Vietnam War.
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.
They controlled North Vietnam, the Ho Chi Minh Trail, and probably controlled the their ally, the VC.
Formally it was two nations: North and South Vietnam. Yes, today it is one unified country (nation)...called Vietnam.
To preserve their nation (the Republic of South Vietnam).