Germany was fucked over by the first world war, Jews were a scape goat for the German people to blame their problems on. Granted it went too far by just killing them, but the country owed so much money to Jewish banks no wonder they hated them. If you back someone into a corner with no real hope for escape, they will go crazy and do anything they can to escape.
Also, history is written by the victor. I'm sure they had their reasons for going to war just like we have reasons for the current wars. People don't fight wars if they know they are wrong, they live and died for the country just like everyone else in the war.
Hitler wasn't the only reason for the war. Frankly it pisses me off when people blame him for everything like he single handedly caused it all. We all are influenced by others, he wouldn't have been able to do it all on his own without thousands of peoples support. When you run a country you do what is best for the country, even if it's an immoral thing. That's why we have army's.