Who launched a propaganda campaign to encourage the resettlement of North Vietnamese Catholics in South Vietnam?

The answer is the USA. The not very many Roman Catholics living in Vietnam around then were the thin cut of their populace that had been participating with their French frontier experts. In those days there was just a single nation and it was called Vietnam and its capital was Hanoi. America set up a manikin government in the southern half and called it South Vietnam and made Saigon its capital. The Vietnamese individuals at long last tossed the USA out and could rejoin their nation.