wolf_brother
Banned
Approximately 110,000,000 people make up European Russia, which is by far the biggest European ethnic group. How late can we break this up into several nations and/or states?
If OTL is any indicator, as 'late' as 1991.
Pre-1900 though I'd have to say the latest would be a total reversal of the Russo-Turkish War of 1877–1878, which even IOTL was a close run. So ITTL instead the Russians fail and the fallout is just as severe as it was for the Turks; ITTL you'll see Romania, Crimea, Georgia, an perhaps even Ukraine break away from St. Petersburg and fall under Turkish influence. Maybe if you get real lucky the Poles decide now's the time for another revolt, and this time they're more successful.
EDIT: Romania, Georgia, and Poland generally aren't considered 'Russian' territories however, and arguments could be made either way even for Crimea. Ukraine however is a core Russian territory; see Malorossiya.