It ended in 1889
Diem, until '63 (he was assassinated the same year as Kennedy). Thieu, until the end.
Probably about '73.
The end of 1969 was the first draft lottery.
The president of South Vietnam at the end of the war was Nguyen Van Thieu.
The Democratic Republic of Vietnam (AKA North Vietnam) .
At the end of the Vietnam War, Congress refused to support South Vietnam any longer.
At the end of the war.
South Vietnam ended in 1975.
Empire of Vietnam ended in 1945.
North Vietnam ended in 1976.