People here are seeming to forget what kind of leadership it requires to convince your people that another group of people must be eradicated. Bat-shit insane? Yes. Excellent leader? Actually, I'd say he was borderline genius in that sense, which would explain the insanity. Also, to note, there's sound strategic reasons behind him doing what he did, although he took it much too far for him to be successful in the long run. Here, let me explain:
When he came into office, he was leading a country that had been ravaged by an unconditional surrender about twenty years prior. Their economy was dead. You think the US depression was bad? They had it worse. Much worse. His people were desperate and needed someone to help lead them out of this time. Enter the Nazis and a man by the name of Adolf Hitler. Now, he and his party helped rebuild their economy. People had job, they had a means to support themselves, and they had hope. Most of all, however, they had pride in their nation. They loved their leader. Want to lead a group? Have them be so enamored with you that they will do anything you say.
Step 2? Create a means by which you can prove to the rest of the world that your country is not one to screw with. So, what's Hiter do? He finds minorities that are already unpopular and start whipping his people into a frenzy to annihilate them by calling them the "source of [Germany's] problems". Enter minority ghettos. Enter "work camps" presented as a means to increase productivity via slave labor. The majority doesn't have a problem with this; their great leader, whom brought them out of the largest crisis any of them had known, said that it was for the best.
Where'd he screw up? He invaded Poland too soon. The Blitzkrieg was an incredible strategy, which would have worked had he had a greater force behind it. Second mistake? He invaded Russia. To date, I can think of only one country that has ever held territory in Russia, and, even then, it was nowhere near Moscow. Sure, the US "saved the day", as we like to say it (we helped, but we were more concerned with Japan at the time), but if there was no England when we came, the European war would have turned out differently. Much differently.
...wow. Campaign setting idea.