I think that if the Japanese had been bloodied earlier, they have understood that the way that wars are fought had changed from their last victory against the Russians, in which superior doctrine had largely won the war. Now, superior technology would be necessary. There was a thread not too long ago about this.
So, here's the idea. The Japanese, during World War I, had a pretty easy run of things, just targeting weak German possessions in the Pacific area. However, they tried to gain greater influence in China (the Twenty-One Demands) and in Russia, but backed out in both instances due to Western pressure, particularly American pressure.
The idea would be that the Japanese decide to carve out a large portion of the Russian Far East and Manchuria for themselves. While not the most economically valuable parts of the world, they will be a valve for Japanese population pressures - settlers will be given incentives to populate the new areas. The Siberian Intervention sees White Russian leaders ostensibly ruling 'Free Russia', but, really, it is a puppet regime for a Japanese military occupation. Sakhalin and Kamchatka are under direct Japanese control, while the Free Territory of the Far East rules the Amur region, and is based at Vladivostok.
In the meantime, Manchuria has been invaded, too. This is particularly upsetting to the Occidental powers. Japan is strongly encouraged to leave, especially by the Americans, but until the end of the war in Europe, little action is ready to be taken.
I also kind of like the idea of the Japanese funding Ungern von Sternburg, who, despite being completely insane, could serve as a significant obstacle to eastward Bolshevik expansion - a buffer, if you will. This would be cool, because I want to tie von Sternberg into this timeline, somehow. I think he has a lot of potential for whackiness.
I don't know which makes more sense: if Japan stills gets to be one of the five countries on the Treaty of Versailles, or not. In any case, I think that by late 1919, the United States should be getting ready to pursue military action against Japan in order to liberate Manchuria.
I think that Britain, which would still be tied to Japan in the Anglo-Japanese Alliance, could go in of two ways regarding Japan. If they have some foresight about the United States being a potentially powerful rival in the future (by the way, I think an Anglo-American War later on in this timeline could be cool), I can see them supporting Japan and maintaining the alliance. They wouldn't go to war with the United States, but they might be willing to rally support for the end of an Japanese-American war, including the signing of a peace treaty and stuff. Is this TOO unrealistic?
I think the war would start in 1920, and not last TOO long. I have not decided who should win, but I'd like it to be a Pyrrhic victory, either way. Either the United States will achieve a variety of strategic victories, but the British will get the world community into believing that a strong Japanese presence in the region is necessary to contain communism; or the Japanese will stun the world once again with several amazing victories (good luck, incompetent American generals), but find themselves militarily depleted and unable to pursue vengeance.
I'd like some thoughts as to how this war would go. I imagine it would have a lot of focus on southern Japan, Korea, and northeastern China.
I want the end result to be a Japan that has experienced the new kind of war, and that has been sobered by the experience. This should allow it to change its military doctrine to something a little bit more realistic than the banzai tactics of the OTL Pacific War. After this war, Japan should perhaps be a
little more satisfied with its world position: the peace treaty will include other countries, and assure that the Open Door Policy is paramount in the rest of China (diplomatic wording ensuring that Manchuria is not really China, per se, but another nation entirely). Looking significantly larger on a map, and with less overpopulation pressure, Japan may avoid the Showa period's rising militarism. Instead of combating the Great Depression with increased military focus, increased focus on settling people on the mainland will take place. Though Japan will still be criticized for the things they do to Siberian natives and to Europeans in the region - I'm imagining deportations, land expropriation, etc. - this will be seen largely as insignificant, and as an internal Japanese problem, like the treatment of Native Americans. I think that the liberal democracy of the Taisho period may last, and the British alliance will certainly keep the Japanese away from the Axis, who may turn to the Republic of China, instead.
Lots of butterflies, in any case, which'll be addressed as we come to them.
So, yeah. A bunch of ideas. They demand intense criticism - however, do see what I am trying to do. I'd like to make a very interesting timeline, and this is a crucial part of it.