OOC: Are you saying that it was a four-sided war between U.K., France, Germany and Italy? Or a two sided war between France + U.K. and Germany + Italy? OOC: OTL as far as I know Japanese did not put much effort into nuclear research. I don't think it is impossible though for there to arise a "Japanese Einstein" in some ATL in the 20th century, leading to the Japanese putting more efforts into nukes. Why would they be "lucky to develop them by the early 50's" in all possible worlds?
OOC: Second scenario but Italy changes sides
Nukes are difficult and expensive, you could buy 20 battleships for the cost of the Manhattan project and Japan was strapped for cash, nevermind that the B-29 program to get a nuke bomber was even more expensive France started a program in 1945 and did not get a bomb till1960, Britain, who was in on the program and did not have to start from scratch, started an independent bomb program in 1946 and took until 1952 to get a bomb, both of these countries have greater expertise in the field, more educated populace, better industrial quality control and more resources than Japan would
Einstein only wrote a letter, he had no real effect on the development of the bomb
IC: RamscoopRaider, I haven't read the book you referenced so maybe you could explain why U.S. goes to war with Japan? U.S. was very big on the idea of isolationism back then and it would be ASB for them to join the World War 2 because of this fact. Japan also never formally joined the war despite liberating a whole bunch of Asian colonies from European influence while the imperial powers where busy fighting each other in Europe.
I guess if Japanese Empire and US do go to war in WW2 and Japanese Empire DOESN'T get nukes while America DOES than it is a Japan screw. I guess
Chekiang never becomes Zion (OOC: Israel in China) so the Jewish refugees never get their own nation but at least decades of conflict between Jews and the local Chinese and White Russian populations. The Soviets probably take the opportunity to finally deal with Von Ungern-Sternberg now that Japanese can't protect Mongolia and turn into an SSR just like they did with Xinjiang just a few years before that. Not sure what would happen to South East Asia and rest of China.
IC: The author actually goes into greater detail, the KMT holds itself together better in the 1920's, so Japan cannot beat the Chinese quickly and they bog down into a quagmire, eventually the US embargos them after repeated atrocities in China, and to get the resources they need to keep fighting they attack the British and Dutch colonies in south east Asia, and they attack the USA as well at the same time to secure their flanks, which is in keeping with their doctrine of the time
So US isolationism really does not get involved, the Japanese attack first and the US responds
You can call it liberating, most refugees, their descendants and local resistance movements call it trading a far away master for a closer and more brutal one