Question

Which city was the capital of South Vietnam from 1954 to 1975?

Answer 1

saigon, however for questions like these you'll probably get an answer much more quickly if you just google it.

Answer 2

Saigon
The North was not interested in negotiations, however, and its tanks rolled into Saigon largely unopposed which led to the Fall of Saigon. Acting President Minh unconditionally surrendered the capital city of Saigon and the rest of South Vietnam to North Vietnam on 30 April 1975.