A great angle to look at US involvement might be Madame Chiang Kai-shek, Soong May-ling (which would be Song Meiling in the modern transliteration system). She was in her way a major figure in America, securing support for the GMD government. Hannah Pakula wrote a biography of her called "The Last Empress" which is an easy, vivid read and also touches upon a number of other things very relevant to this topic: the GMD vs. the CCP more generally, the state of affairs during WW2, America's involvement in both WW2 and the civil war, etc. From there, I'm sure you can find a lot more from Pakula's sources as well.

Regarding US involvement, you might want to check out Forgotten Ally, which details the relationship between China and the US during WWII. It depicts the conflicts that the leadership on both the Nationalist and US side had with each other, as well as the fascination many in the US had with Mao and his forces in the north. Good to get context.

The standard book is Odd Arne Westad's Chinese Civil War

Chiang Kai-Shek wrote a book called "Soviet Russia in China." (1957). Despite his reputation, the man was fairly critical of himself and I would say is relatively objective, considering it was written by a man who had just had his government kicked out of his country and forced to seek exile on a small island. It covers the whole period, including the Sino-Japanese War, as well as actions before the war and his recommendations to stop communism in the future. That said, be sure to keep in mind that he may consciously or unconsciously be self-serving in his book as you read it-he does have a certain bias, seeing as how he would naturally want to make himself look better.