The Class Struggle (Erfurt Program)

Kautsky argues that capitalism's economic development inevitably leads toward socialist revolution, but that this outcome requires the conscious, organized action of the proletariat. He rejects Bernstein's revisionism—the view that socialism could be achieved through gradual reform alone—and also rejects the idea that socialists should attempt to foment revolution before objective conditions are ripe. The party's task is to organize the working class, participate in parliamentary politics, and await the maturation of capitalism's contradictions, which would inevitably produce the revolution.

The book popularized the term 'Erfurtianism,' coined by historian Lars T. Lih, to describe the political outlook Kautsky systematized. More substantively, it offered the Second International's canonical synthesis of determinism and voluntarism: capitalism's collapse is economically inevitable, yet the proletariat must actively organize for it. The book's fourth section, 'The Commonwealth of the Future,' was one of the rare attempts by an orthodox Marxist to describe post-capitalist society, predicting the decay of the traditional family and equalization of wages.

Lenin translated the book into Russian in 1894 and cited Kautsky as the leading authority on Marxism before 1914. He praised Kautsky's Parliamentarism and Democracy (1893) favorably in What is to Be Done? (1902). However, after Kautsky opposed the Bolshevik Revolution and denounced it as a premature coup, Lenin published The Proletarian Revolution and the Renegade Kautsky (1918), attacking his former mentor as a traitor to the revolution. The break was bitter and permanent.

Kautsky emphasized organization, discipline, and patience: the party should build the proletariat's political and economic strength while waiting for capitalism's contradictions to mature. Luxemburg, by contrast, argued in The Mass Strike (1906) that the mass strike was not a tactic leaders could 'decide' but the spontaneous mode of motion of the revolutionary masses. She believed Kautsky's determinism underestimated the creative energy of spontaneous working-class action, and their disagreements deepened over the years.

The book served as the official commentary on the Erfurt Program, the SPD's 1891 manifesto, which made it authoritative for Social Democratic parties across Europe. It offered a systematic, accessible summary of Marxist theory that Marx's own writings—often dense and incomplete—did not provide. Historian Donald Sassoon noted it 'became the accepted popular summa of Marxism' around the world. Lenin translated it into Russian during his exile in Geneva, and Daniel De Leon produced the first English version in 1894.

The book's confident prediction of capitalism's imminent collapse was not borne out in the way Kautsky expected, and his pre-war authority collapsed after 1914 when he opposed the SPD's support for the war. Later critics, including Lenin and Lukács, dismissed the work as 'vulgar Marxism' or 'the Marxism of the Second International.' Yet historians recognize it as the most influential popularization of Marxism before 1917, shaping how an entire generation understood socialist theory.