Western Poland after 1919 was majority Polish, not German, for example Poznan was majority Polish from the 900's until 1900's.
Poznan is the important Polish city where Polish founder, and king Mieszko I was baptized to Catholicism, and had united the Polish Lechite tribes under the Polish banner.
Poland fought for Poland in the Greater Poland Uprising of 1918, The Treaty of Versailles merely finalized what Poles had fought for.
Actually, Germany was nice enough to create a Polish state out of the territory in Russia they took, and then the Poles stole a bunch of land from them at Versailles. Then they stole land from Russia in the Polish Russian war of 1920.
And then they wondered why Germany and Russia crushed them like a bug!
Joeb's is leading this topic off the tracks, I fail to see what the Gdansk Corridor has to do with Katyn Massacre by Soviets.
Okay.
Germany makes a REASONABLE request to return it's territory.
The Polish Colonels (Poland wasn't a Democracy at that point) decided they were going to play tough and made an alliance with France and the UK after they sold out Czechoslovakia.
Germany makes an alliance with the USSR to divy up Poland and they would both get lost territories back.
The Polish Colonels and other officer run into the Soviet Zone, and the Soviets decide they don't want these idiots stirring up more trouble.
Oh, well. Maybe if they had been reasonable to start with.. it wouldnt' have gotten this far.