The training of the japanese military was unlike the training of any other great power military. It will require many more layers of diplomatic cover to conquer or control areas in the twentieth century. In the old dayse you could just take hem over while there are still powers that live by the old rules. And there will be a public opinion price for doing that.
The Asia-Pacific War of 1937-1945 has deep roots. It also involves a Japanese society that's been called one of the most distinctive on Earth. If there were a Japanese version of Captain America, this would be his origin story.