Arthur Rosenberg’s remarkable essay, first published in 1934, was probably the most incisive historical analysis of the origins of fascism to emerge from the revolutionary Left in the interwar years. In contrast to the official Comintern line that fascism embodied the power of finance-capital, Rosenberg saw fascism as a descendant of the reactionary mass-movements of the late-nineteenth century. Those movements encompassed a new breed of nationalism that was ultra-patriotic, racist and violently opposed to the Left, and prefigured fascism in all these ways. What was distinctive about the fascists in Italy and Germany was not so much their ideology (a pastiche of motifs that drew on those earlier traditions of the conservative and radical Right) as the use of stormtroopers to wage the struggle against democracy in more decisive and lethal ways. After the broad historical sweep of its first part, the essay looks at the factors that were peculiar to the Italian and German situations respectively, highlighting both the rôle of the existing authorities in encouraging the fascists and the wider class-appeal of the fascist parties themselves, beyond any supposed restriction to the middle-class or ‘petty bourgeoisie’.