Tuchman appears to be attempting two disparate things with this book: to tell the story of Joseph Stillwell's career in the military and to tell the story of US intervention in China from the (first) Chinese revolution to the expulsion of the Kuomintang. She succeeds at the former a lot more than the latter, in part because this book is just way too US-centric. Tuchman does a remarkable job of trying to understand Chinese culture, but at the end of the book one still feels like one is reading a history of China written by an American and primarily concerned with China as perceived by the US. Tucchman doesn't quite give us a biography of Stillwell - his early life is very briefly discussed and the majority of the book focuses on his experience in WWII - and she doesn't quite tell the story of the US experience in China - the earliest interventions are given as back story and US involvement in the end of the Chinese civil war is denouement - but there are still some very interesting things to learn in this book.
Stillwell comes across better than I think most generals of his rank would: he once personally risked his life - and his Chinese batman - for what was essentially a spy mission he knew needed to be accomplished, and he once successfully led survivors out of a jungle on foot when his superiors thought he should have flown out weeks prior. Neither of these things makes him a hero necessarily; I am not trying to say that. Rather they make him relatable as a human being: more than many - most? - generals, Stillwell appeared to be unwilling to commit people to do things he himself was unwilling to do, and that makes him far more relatable to someone like me than most soldiers and especially most generals. And Tuchman lets us see that Stillwell had very good reasons for his "vinegar" personality and very good reasons for holding the opinions he held. He comes cross as someone who may have been acerbic, but who had every reason to be. And though Tuchman takes Stillwell's side with regard to Chennault and Chiang - and she is right to do so - and to some extent the British - less obviously correct - she doesn't take sides with regard to Stillwell and Roosevelt, which is, I think, the right thing to do.
As for the bigger picture, Tuchman clearly wrote this book with the Vietnam War in mind - it was published during it - but she fortunately never hammers that into the reader's head; the reader is left to draw conclusions on his own. The huge snafu that was American intervention in China should provide numerous lessons for American interventions in Vietnam, Central and South America, and Iraq and Afghanistan. What is the biggest lesson? Don't do it. The United States put in billions upon billions worth of resources and expended time and energy of numerous people with the result that a fascist regime lost to a communist regime. That's all that resulted. In the interim, as many or likely more people died than would have had they kept their hands out of it. One can certainly debate the merits of US intervention on the side of the Chinese from 1937 through 1945, but the intervention prior to 1933 and from 1946 was just a giant disaster - as anyone who studies history enough should have been able to judge ahead of time - and should serve as a future lesson: it doesn't matter what your intentions and what your resources, countries and cultures don't change just because you want them to.