Poland had been split 3 times by a Prussian+Austrian+Russian alliance long before WW2. Some of those nations were even trying to forcibly transplant their own culture in Poland.
This is a great lesson for all those playing Civilization-like games.
Don't start a country on plains without any mountains or hills blocking access from at least 3 sides.
Poland was unlucky by having mountains in south, where we have rather peaceful nations. Sea from north (Swedes invaded Poland once, but that's mostly it) and nothing (except forests) from west (with Germany) and Russia in the east.
(of course now it is a bit different, but lack of natural obstacles from east/west is still real).
