This will become a practical test for the rainbows and unicorns organization that is supposed to prevent aggressive war. The league of nations has to respond to it. They send investigators in 19 32 y to look at the train tracks that were blown up and examine everything. And while they're doing this, the japanese militaryis creating a puppet state they're going to call manchu quo. But the rest of the world is going to say, you can't keep it.
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.