An improbable post in After-1900 got me thinking and I couldn't find anything in search or on Google, so...
1, Challenge: With a POD after 1700 and before 1871 give me a scenario or group of scenarios in which Russia and Prussia and/or Russia and Germany are united in a full political union. Preferably the latter, but it can at least begin with the former.
Bonus points for a Hohenzollern-Romanov dynasty, of course.
2. Please provide your opinion on the effects and future of such a Union in history. Surely there will be a succession war, but I want the Union to win obviously.
Cultural, military, linguistic, etc.
Let me hear ya.