Vietnam was not a US war of aggression: the US came at the request of the French presence as the communist north tried to take the French allies in the south. The result was a mess, sadly, predictably.
Nonsense. As if one colonial power asking another to come slaughter the population would make it any less aggressive.
The French agreed to leave and support elections with the Geneva Accords. The U.S. propped up a dictator and organized a campaign of brutal suppression and terror, then outright bombed the hell out of peasants in the south starting in 1962 under JFK to block a political settlement. That's as aggressive as it gets.
Are we talking about the American-Vietnam war or the Sino-Vietnam war? If the latter, China wanted to give Vietnam a taste of Chinese freedom for something going on in Cambodia.