[2] The motivating force behind his scholarship was that academia must counter the idea that "...anarchism represents a criminal sect which lacks any social or political programme..."[3] According to one historian on German reformers, Diehl had acquired a reputation as the "most important authority on socialism, communism, and anarchism," comparable only to Werner Sombart.
Joseph Schumpeter, the well-known economist, has praised Karl Diehl for his understanding of the mutualist Pierre Joseph Proudhon, writing "Of the Proudhon literature, I mention only a work of indubitable scholarly quality, though there are several others that come within this category: Karl Diehl's P. J.
[8] In 1890, Diehl came to realize that William Godwin was the father of the Anarchist movement and theory,[9] early sparking his interest in this area of thought.
He is quoted by one editor in a volume on German Anarchism as saying... Anarchist ideas evoked a certain amount of theoretical interest and discussion.
But the anarchist movement in Germany never achieved any significant political activity, nor did the group organizations at any time approach a numerical size which could be considered important.