The 'Ezo Republic' survives on Hokkaido, as a French protectorate: Originally it's a democracy, more or less, although only members of the Samurai class have the vote. Imperial Japan annexes it in the late 1930s, triggering a war with France that Japan wins and from which Japan also gains either Tonkin or Cochin-China (I haven't decided which...). This in turn triggers a greater drive towards military improvement in France, but that's too late to do the country much good before Hitler -- encouraged by the apparent weakness that France had shown (defeated by a bunch of Asiatics!) -- starts WW2 more-or-lesson "on [OTL] schedule" anyway. There are some minor effects on the course of WW2, but this still ends with an Allied victory. Afterwards, France is too busy rebuilding at home & re-establishing control over Indo-China to take much interest in Hokkaido, and the Ezo government-in-exile is returned to power by the WAllies with Stalin (who hadn't been able to organise a "liberation" for that island in time) bought-off by recognition of a Soviet sphere of influence in Manchuria & outright control of Port Arthur. Britain and the USA insist on the republic adopting a more democratic constitution, and it replaces the old unicameral 'Senate' with a bicameral Congress in which the Samurai now control only the "upper" chamber while the "lower" one is elected by universal suffrage instead. This state benefits from hosting American & other "UN" facilities during the Korean War, and even sends a small force to participate during the final year of that conflict, but then declares neutrality in 1955 -- the same year in which it joins the UN -- and refuses to host any further foreign military or naval installations during the Cold War. It does, however, welcome tourists for whose benefit aspects of the traditional Japanese culture are displayed.
(NB: In this timeline the Russo-Japanese War still happens basically as IOTL, but the Kurile Islands belong to Ezo all along --except during the [1930s]-1945 Japanese takeover -- while Russia holds all of Sakhalin.)
Reminds me of the Aberystwyth books and the Patagonian War.
Ah, yes: "Patagonia, the Welsh Vietnam" as that series' protagonist phrases it.