General Claire Chennault did everything he could to convince the US to stay in China and fight the communists, but he was unable to, for 2 reasons:
1. The US military brass hated Chennault.
2. US politicians considered Chang a dictator.
So, petty office politics doomed China to communism. As an American I feel awful about it, because we could have stopped it but did nothing. Most Americans don't even know that we had a huge air force right there in China and an American General chomping at the bit to bomb Mao to hell.
Nothing we can do about it now...
Sorry we abandoned you, China.