I was trying to come up with a scenario involving a communist Japan and it seems I may have struck it with this one. Is it plausible that Japan not backing down to international pressure to turn China into a suzerain in WWI would have drained the country dry enough and made it enough of an international pariah to face collapse in the 20s/30s? Butterflies would probably be minimal enough in Europe. America may not respond too well though...
No. This is fairly unlikely.
Imperial Japan in the Great War era arguably didn't have the milliterist faction at the head of government, hence is far less of a warmonger state than it would become.
Secondly even though the 21 Demands were rejected and a debarcle, during the Great War Imperial Japan had been able to gain several new terrirorities for itself even without enforcing a defacto puppet relationship over China. If Japan stood up to the Allies or Americans by 'pressing China' there was a fair chance that the British or American fleets would sail over to the pacific, and the British and Americans 'enforce' both trade sanctions, and/or apply gunboat diplomacy to annex these captured ex-German territories from Japan, in order to bring Japan to an accord.
In which case there is huge loss of face. Thus it was never on the table.
Had the Imperial Japanese Diet gone ahead with full war in China circa 1918, then it is more than likely that Japan would have fully occupied Southern Manchuria, the Shangdong and Shaghai penisulars as well as likely captured Hainan and moved on Beijing and possibly Nanjing.
The Chinese at this time would have been powerless for the most part to do anything about this.
Internationally the move would likely be very much condemed, and would lead to the enevitable breaking of the Anglo-Japanese allience, as well as a freezing of relations between the powers. However Japan having full access to Chinese markets and authority (at least in the coastal regions). Means her stability will get much stronger in the years to come.
Since Japan will have 'gained China' as her 'puppet' the politics of the 1920s for Japan that favoured co-operation rather than belligerentism towards China will bear fruit, and by circa 1930 when America enters the Great Depression Imperial Japan will be far less effected because she has well developed access to the Chinese markets.
Thus a stable Japan is in exsistance, the Japanese milliterists will not have the economic troubles to gain power, and the strong conservative push of the 1920s Japan will continue through the 1930s. It is likely that Imperial Japan would stay out of a second world war, and would later come to be a staunch supporter against the communists during the Cold War.
The 'Communist Japan' angle is best served by having OTL events up until the late in the war and having the Russians invade/bomb/control the Japanese mainland ahead of the Americans. But that has other repercussions too...
