I find it very interesting that all of you chose to ignore ANY of Germany’s pre-20th century history. From the Polish perspective, the 1939 agression was nothing new. Germany was ALWAYS an extermely agressive neighbor to just about everybody. In 1000 years of coexistence, there was only about 300 years of peace between Poland and Germany. By contrast, the longest peaceful coexistence in the world between neighbors was recorded between Poland and Hungary (well, at least without an open war; there were some minor hostilities). So, the fact that Germany would attack their neighbors was just a matter of time and timing.
In my opinion, the only reason there was over 60 years of peace since 1945 (little more than an eyeblink in the context of the previous 1000 years) around Germany were 2 facts 1) Soviets kept everybody at bay in Eastern Europe, 2) Germany DID suffer a crushing defeat in WW2.
Sooo, it was the fact that Germany was (is) Germany, that caused WW2. Or, from the perspective of recent events, democracy. After all, Germans freely elected Hitler, right ?