I think the whole thing was complex, but a couple of factors were very important in what happened. One is simply centuries of ingrained anti-semitism, common to all of Europe, some places worse than others. Another factor is that European Jewry were a convenient scapegoat for the Nazi regime. Nothing works better to get a group of people together than to give them a common enemy or cause. The Nazis were able to get people to unite against the Jews. This was all part of their massive propagande machine. Of course a huge motivating factor was the enormous financial gain achieved from the persecution of European Jewry. The art works, gold, property, and other goods stolen is still the subject of debate today. The Swiss banks still refuse to explain how they came into possession of much of it. Precious art owned by certain parties can be traced back to Jewish pre-war families but is not yet returned. Some countries (Lithuania) have stalled or outright refused to give back what was taken to the Jewish survivors during the war. I think the power of money was absolutely key in the destruction of European Jewry.