The Vietnamese beef with China is so ancient and acrimonious that even though we fought a bloody war with them which still exists within living memory, it's already largely water under the bridge, a mere blip compared to their icy relations with China which are older than our country multiple times over. Ho Chi Minh didn't even really want the US to be his enemy, but when we came in to prop up France's colonial mess he didn't really have any other option than to turn to the Communists for help.