Re: "... the Chinese decided that, VietNam belonged to them they invaded ..."
Yes, indeed, though that is not the full answer either. The point is that China, being the regional power, has always had designs on local territory, has acted in such a way, and there has consequently been much strife.
How would I come to have such a strong interest? One of my brothers did much to resettle Vietnamese refugees in this country, I learned from them, from him and from books.
Returning to the point, the US cold shouldered the Vietnamese - presumably because they regarded France as both a mentor and ally in the democracy states, and the Statue of Liberty points in that direction, though they were made to pay for it! - and they approached the eastern bloc as a consequence. The main thrust of my point was that the war could have been obviated with just a little common sense. When China assumes the American position in world economic and military power stakes, well I am not very comfortable with the thought. That's where my thoughts were supposed to have led you. I am sorry if I failed in achieving that goal.
Finally, the Chinese /were/ repulsed. It's something of a military lesson sometimes taught to people like me, in their (one time) military capacities. Cannae, Trafalgar, lots of lessons to be learned, especially in Vietnam and other resource stretching wars, such as the north African desert, which posed similar problems for the British in WWII.