I read Tuchman’s book a few times. She seemed to think that we could have kissed & made up with Mao’s communists. I don’t think that was ever going to happen.
One facet of Chinese character that came through was how thoroughly corrupt they are. Also, their total contempt of foreigners. Chaing Kai Shek opened the windows to air out his office after a visit by Stillwell to “remove the odor of the foreigner.” I loved Stillwell’s characterization of Chaing Kai Shek as “Cash My Check.”
It seems that about every 30 years or so, the Chinese go through a huge wave of xenophobia and isolation. They get a collective desire to purge everything foreign out of Chinese society. It happened during the Boxer Rebellion, the Civil War, and the Cultural Revolution. We are overdue for another such event, I think.
The sense I got from the book is more that we could not influence events on mainland China in any important way period. The Japanese invasion was a complication for both the Communists and the Nationalists, but both camps figured that in the end the Japanese would be defeated by the allies so they wanted to save their strength for the inevitable post-WWII civil war. Both camps wanted U.S. economic aid but without strings. I don't remember that Tuchman made a case that we would have done any better pouring resources down the Communist rathole than we did pouring them down the CKS rathole.