After World War 1, Japan grabbed parts of Siberia, Manchuria and hundreds of formerly German held islands.

There was a huge earthquake and subsequent fire that destroyed Tokyo on September 1st, 1923.

Here I quote a 1928 atlas from its article about Japan, after it mentions the then recent earthquake:

"The old saying which everyone is familiar with: "It's an ill wind which blows no one good," seems to be the case so far as the Japanese disaster is concerned. The United States seems to have been selected by a divine providence as the beneficiary of the Almighty in reducing Japan through the recent disaster to a state where she may, be considered as impotent to take up arms against the United States for at least ten years, it is estimated. It had been reported by military experts of the United States the Japan, prior to the earthquake, was preparing for a break with the United States and it was thought that they would strike during the years 1924 to 1927. With the rebuilding program ahead of Japan, thrift and saving, among both the government and people, alone will make it possible for Japan to revive."

The tone probably doesn't sit comfortably in modern ears, but remember this was written by an American over 90 years ago.

No, your missing my point. I'm not saying nationalism didn't cause the war, I'm saying it seems more externally driven than internally. Japan going to war was about becoming a major power and putting it in a position where it couldn't be colonized by external powers vice maintaining power by creating a common adversary. The incident in Manchuria surely wouldn't have been possible without those circumstances, but it also wasn't engineered to strengthen the Japanese ruling elite.

Unpopular fact, western countries including the US,UK fully supported Japanese imperialism and expansion until shortly before Pearl Harbor.