Karl Kautsky’s works of history have been unjustly forgotten by the Left. In the wake of Vladimir Lenin’s fierce polemic, The Proletarian Revolution and the Renegade Kautsky, the intellectual who had once been described as the “Pope of Marxism” very quickly became yesterday’s man.

This was a regrettable turn of events. Not because Lenin was wrong in what he said about Kautsky, but rather because he was right. In order to defend his political actions during and after World War I, Kautsky retreated from the strongest elements of the version of Marxism he had helped develop in the decade or so following the death of Friedrich Engels.

At the turn of the last century, Kautsky made an important contribution to historical materialism that had a positive influence on the works of Rosa Luxemburg, Leon Trotsky, and Lenin himself. Alongside his seminal study of the agrarian question and his key essays on American and Russian social development, the best works of Kautsky include his books on the history of Christianity, from the early Church of the Roman Empire to the radical proto-communist sects of the Reformation. It is those writings I will discuss in this article.