Hannah Arendt, The Origins of Totalitarianism. Also Kurt Sontheimer, Antidemokratisches Denken in der Weimarer Republik:
'In its name National Socialism united the two most powerful ideological impulses of the epoch. It already conceptually anticipated the synthesis which the era had yet to accomplish. The old-style socialist parties were not national, the national-bourgeois parties not socialist. But this seemed to be the party which was both and simultaneously the party of Germany's future.'