Percent of Jews in Poland (in 1931) by county / city, compared to former borders between Prussian, Austrian and Russian Empires:
That was caused by mass expulsions of Jews from Prussia by Frederick the Great, Frederick William II, Frederick William III, etc.
In general - expulsions of Jews by these Germs from Germ-any.
Here is what a modern Jewish historian - David Solomon - said about Jews and Germ-any during one of his lectures:
"(...) The Shoah is not an isolated event. The project to exterminate the Jews of Germany happens here [pointing at the timeline of history], and here, and here, and here, and here, and here. And so people say - so why did Jews keep going back to Germany? Why did Jews keep going back? And I say - look at your own generation. Only half a century after the Holocaust, and what is the largest growing Jewish community in the world outside of Israel? It's Germany. And yet surely the lesson of this entire wall [pointing at the timeline of history] is that Jews should not be living in Germany. We hope and we pray... in the end of the day, in hundreds of years from now, I'm hoping that... well, if I'm starting to explain that more I'm gonna get further and further into problem, so I'm gonna stop, let's go back to history (...)"
Here is the lecture in question (and the excerpt I quoted above starts at 0:55:50 and ends at 0:57:10 of the video):
Germs probably have Anti-Semitism in their genes.