" For an ideology differs from a simple opinion in that it claims to possess either the key to history, or the solution for all the " riddles of the universe," or the intimate knowledge of the hidden universal laws which are supposed to rule nature and man. Few ideologies have won enough prominence to survive the hard competitive struggle of persuasion, and only two have come out on top and essentially defeated all others: the ideology which interprets history as an economic struggle of classes, and the other that interprets history as a natural fight of races. The appeal of both to large masses was so strong that they were able to enlist state support and establish themselves as official national doctrines. But far beyond the boundaries within which race-thinking and class-thinking have developed into obligatory patterns of thought, free public opinion has adopted them to such an extent that not only intellectuals but great masses of people will no longer accept a presentation of past or present facts that is not in agreement with either of these views. "