Salutations All
To add my two cents worth.
This is hard, Japan does not attack Hawaii, well from this point of view if the Japanese had not attacked Hawaii and other US Territories (Philipines) it would be hard for the US Government to garner support from the average joe on the street just to give a damn of what the Japanese were doing in China, send advisers and a small volunteer force of mercenaries like the Flying Tigers is something that the US get away with, but full scale military deployment and a declaration of war on Japan. This means that the USA would have to be the one to strike first
Again this could also relate to Europe.
Regards
Roddoss72