He took a nation embarassed by the outcome of WWI and the Versailles treaty, in a really bad economic position, and promised to turn them into a world power. Also, he was a very charismatic speaker as was stated in some other posts, and he played on the fears and hopes of a demoralized nation. These people were willing to grasp on to any ray of hope, even though he himself was not even German, Aryan or anything like that.