This reinforces my belief that the only worthwhile game (for experienced players) involves 8 humans...
I recommedn you duplicate this feat with IGC2.1/v1.09 Very Hard/Furious.
I attempted it as Russia but I was stymied in two regards:
1: The Time of Troubles... in between 1602 and 1612 My government fell 3 times and every terriotry I had painstakingly conquered went independent, and some new ones were formed (Ukraine...) the only state which didn't go independent was Novgorod, and that's because I carefully guarded it with half my army.
As a result, I had to spend the next 30 years re-acquiring all my wayward possessions.
2: China... MUCH tougher. Thinking that China would be a pushover (as it had been in my standard GC games), I carefully gathered a large force on their border in about 1640 with several decent leaders. I was shocked to discover that China had NOT ONLY lvl 4 fortresses, but several 100 strong armies and aggressive land tech.
I made no progress. The war ended eventually in a white peace with my entire eastern army destroyed. So I fortified the Chinese border and let sleeping dogs lie after that. I should have clued in after China annexed both Japan and Dai Viet, followed later by Ayahuttyha.
End of game I controlled 90% of Europe, 100% of Siberia, and the Chinese economy was the same as mine. Shocking.
Probably if I tried it again I could devise a way of defeating China, but it looks like a LOT of work.