I don’t know if that’s true.
In the War of 1812 we were allied with Napoleon against England. Japan & Italy were our enemies BECAUSE OF WWI, not in spite of it; both felt they had been short-changed by Versailles. The Soviets were hardly an ally in WWII; while the Japanese invaded Alaska the Soviets had a peace treaty with them (until the final months of the war). “China” in the Korean War was the Red Chinese, against whom we had armed Chiang Kaishek; our ally “China” was on Taiwan/Formosa by that point (having lost the civil war in 1949). India is still “non-aligned”; we probably still have more military interaction with Pakistan (as long as they have an officially-secular government we will work with them).
In any case, it doesn’t make it any easier to understand why we’d have such cozy relations with the Hanoi government.
Well, when I was talking about the French and “15 years later”, I was referring to the Quasi-War.