It would hardly be a new development - politics makes strange bedfellows. In the Revolutionary War, France and Spain were allies - just 15 years later we found ourselves at war with the French. In the First World War, Japan and Italy were our allies, and in the Siberian Expedition, the Soviets our enemies. In the Second War, 23 years on, the former friends were our enemies, and the Soviets and Chinese our allies. Two years after the war’s end, the Soviets had become our dire foe, and another three years after that the Chinese were as well, while the Japanese were slowly becoming our valued ally in Asia. Just 30 years ago, India was a Cold-War foe, and Pakistan an ally. Now India is becoming rapidly aligned with the US, and it is Pakistan that has become more and more an enemy.
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.