Revolutionary Variants of Classical Marxism Arose

Out of all this, revolutionary variants of classical Marxism arose. Several made their appearance at almost the same time. After the death of Friedrich Engels in 1895, no longer was there an authoritative control over developments of what might pass as ideological orthodoxy. Almost immediately after Engels’s death, Eduard Bernstein’s first efforts at theoretical revision made their appearance. There no longer was an “official” guide for what was to be considered Marxist “orthodoxy.” The result was a rapid unraveling of the dense ideological system as it had been left by its founders.

--A. James Gregor, Marxism, Fascism, and Totalitarianism: Chapters in the Intellectual History of Radicalism (Stanford, CA: Stanford University Press, 2009), 48.