Horkheimer and Neumann diverged because philosophy-of-history and reformist Marxisms framed fascism differently

Evidence

At this point the two were talking at cross purposes. Horkheimer was a theoretician of integral statism whose approach to Marxism was through the philosophy of history; Neumann was a theoretician of totalitarian monopoly capitalism whose approach to Marxism was a reformist one. — Rolf Wiggershaus, The Frankfurt School, 307

Categorization

• DEFINE: Cleanly labels the two theoretical positions — integral statism versus totalitarian monopoly capitalism — that split the Institute.
• XREF: Ties back to the Horkheimer-Neumann ‘incompatible versions of Marxism’ split noted earlier in the book.