According to a housemate back in the '60s, who was from Hue, Vietnamese history had a succession of dynasties. When one dynasty became enfeebled and corrupt, some new guy would come along, overthrow the King, and start a new one. Part of Ho Chi Minh's acceptance was due to the fact that he was regarded as potentially such a founder of a new dynasty.
I would not depend on facts from a housemate.
Concerning Ho Chi Minh, he was not of Royal Blood and he could not establish a Royal Dynasty.
Ho Chi Minh did however by force establish a Communist Regime in North Vietnam, that in time invaded South Vietnam and united the country under Communism.
Concernig the history of the Nguyen Dynasty and succession of dynasties information can be obtained here:
http://users.panola.com/vietnam/crown.html