Nixon opened our doors to china.
Your understanding of history is infintile.
FDR took the advise of Communist spies and abandoned Chek in favor of one of history's two biggest Mass murderers, Mao (FDR's "Uncle" Joe being the other).
I think you need to check your history.
FDR died in 1945. The communists didn't win until 1949. No one abandoned Chiang Kai-shek. In fact, billions were spent to prop him up. The only thing FDR did was emphasize that beating Japan was a little higher on the priority list than wiping out the last of Mao's forces.
Here's the dirty little secret about Chiang. The guy was a Nazi. In fact, he was such a fascist Hitler and Mussolini seriously considered inviting him to join the Axis instead of inviting Japan. Then they figured Japan was the better bet.
Also, like most Americans, you tend to overemphasize our importance. In fact, the Russians and the Chinese had a lot more to do with beating the Axis than we did.