Your challenge, should you choose to accept it, is to craft a scenario with a POD no earlier than 1790 wherein the Kingdom of Prussia and most (if not all) of Europe's Polish-speaking lands are united within a single state.
There must be significant legal protections for either Germans or Poles, whichever the situation necessitates.
There must be significant legal protections for either Germans or Poles, whichever the situation necessitates.