DBAHC: Russian Prussia

I assume you mean East Prussia, not all of Prussia, no? Frankly, I don't see how this could happen. Yes, their invasion during the Great War might have been more successful, but why would they want to keep it? More importantly, how? Poland's trouble enough already, and you want to add several million Germans to the mix? They would have to drive them all out of their homes and replace them with Russians, and that's simply not how civilized states behave.
 
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