We basically defaulted, never a battle lost, to the North because of incompetent and later treasonous leadership and conduct by a Democrat president and Congress, and a fifth column press. But when China tried to push her little neighbor around she got her nose well bloodied. And the reasons why it would be advantageous for us to develop a relationship with a country adjacent to China, with several excellent seaports on a thousand mile long coast line, ought to be pretty obvious. To the Vietnamese I've met overseas the war is ancient history and they crave a new relationship with us. Personally, I think having one with them is long overdue.
China? I believe you have mixed up WW 2 and Korea.