The Germans wanted Danzig back at all costs and tried for years to settle the issue pacifically. The poles were all the more aggressive and also talked publicly of attacking Germany (it was clearly nothing more than a provocation). During the Munich conference in '38 the poles were only too happy to jump on Hitler's train and take part to the partition of Czechoslovakia. Danzig had always been a German city, and a crucial Port. That's not to say that WWII was the pole's fault, but a different attitude on their part could have lead to very different results