It was honestly a Freak Chance, Republic of China quickly collapsed due to both Warlordism and Qing Loyalism before Japanese quickly took control due to mixture of technological advantage, religious fanaticism, and let's not forget that for all their faults, the Chinese peasantry did actually receive Japanese troops with open arms.
And US choosing to back the very unpopular Chiang Kai Shek, that was already regarded as American Puppet, and at the same time, Philippines' Revolt happened. And it took Japan 10 years to wipe out American Pacific holdouts and the end of the war happened only due to threat of British intervention on Japanese side.
The Pacific War was mix of utterly bad luck piled on USA. Any of those bad things not happened and US will stomp the rising Empire of Japan.