Dear AlexanderG!
Well, I'm afraid this AAR outcome is more realistic for Russian situation then your reasoning. Russia is rather "defense-minding" country & Russians according to history fight better on their own territory. Examples:
1. You told us - Austria didn't surrender losing to Russia her "3 capitals". Well, the same thing was for Prussia losing around 75% of their territory for Russia in Seven-Years war & Frederick the Great didn't ask Russia to make Peace - Russian ruler asked him - try guess why? Why Prussia didn't surrender? Why Russia make "White Peace" pretty fast?
First answer is - German population was... they didn't like Russian attitude to occupied populace - then Russians need to garrison taken Prussian cities pretty heavy as a rule. It wasn't "silent resistance" on Peasant/"commoner" level famous Phisosopher Immanuil Kant didn't succumb to really hard pressure in asking to join "Konigsberg occupation magistrate" preferring rather long (but mild) imprisonment with librarian occupation for taken in custody. It means - Prussian majority wasn't happy with Russian occupants as national entity then Friedrich didn't make peace negotiations at all.
Second answer is - victorious Russia in mid-XVIII century was on brink of collapse. If you check Russian History more closely - you'll find out about a series of mutinee swept around this country in form of "Salt, Copper" & most gross - "Cholera Mutinee" in Moscow with "Peasant War of Pougachev as result". I'm far from spaeking - Russia was on brink of great Civil War in mid XVIII century, but all processes are resembled processes of XX century.
2. From another point of view - all "glorious Russian wars" (against Swedish King Karl XII, Napoleon, Hitler, or - various Polish/Lithuanian invaders in EU2 timespan) began from big territorial losses for our country, but instead of seeds of dissent we've got a real hard & harsh flame of Patriotism/Nationalism supported by preaching of jealous & fanatical "Orthodox Religious Order of Muscovy" (named so by some Russian historians).
3. All lost wars of Russia were on her national borders without significant Russian inhabitants & Russian majority saw them as "not ours war" - this description belong to various Azov rackets of early Romanovs, European & Caspian war-tripping of Peter the Great, Seven-Years War, early Napoleonic wars, Crimean war, Russia-Japan war & Afghanistan story if you like the parallel. All these wars rised really gruesome seeds of discontent in Russian population with rather long periods of national disturbance after them.
A. Are you wonder if Communist system broke apart - rather unexpectedly, egh? What do you say if I tell you - reason was in unpopular & unfruitful war in Afghanistan? Do you agree with next statement - Communist system had some faults & unsuccessful military efforts in Afghan broke spine of Russian Red Colossus?
B. Are you wonder if Czarist system broke apart - rather unexpectedly, egh? What do you say if I tell you - reason was in unpopular & unfruitful Fisrt World War against Germany? Do you agree with next statement - Czarist system had some faults & unsuccessful military efforts in lost Poland broke spine of Russian White Colossus?
Then - if Russia lost her territory very heavy in Campaign 1914-1915, then we could get the same scenario as - with Karl XII, Hitler, or Napoleon. But - according AAR she was winning - then we've got another Crimean war/Seven Years War/WWI/Suvorov March through Alps scenario. It's - simple. It's - SO SIMPLE.
Russian "Great" wars never was about - territory, or monetary gains - our country has territory enough & any spoils of war never reached common Russian soldier ;0. It was about common people attitude to this war & they like to fight only in case of mortal danger to all dears for them. It's - SO SIMPLE.
Brgds, Alex Bash.
P.S. By the way Russia lost her cause not in mythical counter-offensive in 1917. She lost bloom of her Nation & Officer Corps in Victory of so named "Brousilov Assault" of 1916. Do you know - any honest Officer didn't like "to shake hand" with this general & he got nickname as "Butcher". It was a main reason for him to convert on Red side under first available moment. Do you know... 15-16 years youth of nobility had to take command in Russian Army after this Brusilov "success". Soldier masse went out of control from these unexperienced hands - pretty fast - it became dawn of chaos - Revolution occured half year after that

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