Germany didn't exist until the 1870s. Prussia was a German state for three hundred years before that, having been slowing encroaching on the Polish-Lithuanian Commonwealth. Prussia and Austria, with the help of Russia, annexing Polish land doesn't count as it being "always German."
Hell, in Roman times the land wasn't German at all. There was even a substantive Celtic presence.
The point, though, is that "Muh clay" is not an argument. A single document with collected quotes about how evil Poles are proves exactly jack shit.
Let me guess, you believe Germans are evil too? After all, there are many people quoted on the evils of the German, and just think of their unjustified persecution of their minorities! Trust me, this unsubstantiated document says so! I have a letter from a totally real Jew complaining that all his rights were deprived in Germany and that Germans were incited to murder and mob violence against Jews.
If anyone actually believes this horseshit they must believe the Holocaust was real too. After all, listen and believe, right?