Hitler knew communist Russia was going to invade Europe. That's why he beat them to the punch and he almost made it to Moscow despite the extreme winter conditions. Poland was killing and abusing ethnic Germans who lived in the Danzig territory which was taken for reparations after WWI. Hitler worked tirelessly to come up with a peaceful concession with Poland but they refused and forced his hand. Also we now know that the US was telling Poland not to accept any agreements with Germany because they would support them if war broke out. If you want a very good book on the truth of Germany's struggle post-world war one, read Hitler's Revolution by Richard Tedor.
The brown shirts were the forerunners to the SS.
https://en.m.wikipedia.org/wiki/Sturmabteilung
Poland was killing and abusing ethnic Germans who lived in the Danzig territory which was taken for reparations after WWI. Hitler worked tirelessly to come up with a peaceful concession with Poland but they refused and forced his hand.
Also we now know that the US was telling Poland not to accept any agreements with Germany because they would support them if war broke out.
If you want a very good book on the truth of Germany's struggle post-world war one, read Hitler's Revolution by Richard Tedor.