Fun fact: Hitler's actual plan when he invaded Poland was to reproduce the trench war stalemate of WWI on the Western front. He knew that in that war, about 2.5 million German soldiers had been able to stymie more than 4 million French and British troops while the remainder of the German army pillaged Russian territories. This is why during the Winter of '39/'40 he devoted almost half of German productive capacity to making artillery shells that mostly ended up not being used until the later invasion of the USSR. His biggest success of the war was the blitzkrieg of France, and it was absolute blind luck (mixed with French ineptitude and lack of preparation) that it ended up going the way it did.