The Erfurt Program was adopted by the Social Democratic Party of Germany during the SPD congress at Erfurt in 1891. Formulated under the political guidance of Eduard Bernstein, August Bebel, and Karl Kautsky, it superseded the earlier Gotha Program.
The program declared the imminent death of capitalism and the necessity of socialist ownership of the means of production. The party intended to pursue these goals through legal political participation rather than by revolutionary activity. Kautsky argued that because capitalism by its very nature must collapse, the immediate task for socialists was to work for the improvement of workers' lives rather than for the revolution, which was inevitable.
Erfurt Program Wikipedia
Karl Kautsky also wrote the official SPD commentary on the program in 1892, which was called The Class Struggle. The simplified Marxism exemplified by The Class Struggle is sometimes referred to as 'vulgar Marxism' or the 'Marxism of the Second International'. The popular renderings of Marxism found in the works of Kautsky and Bebel were read and distributed more widely in Europe between the late 19th century and 1914 than Marx's own works. The Class Struggle was translated into sixteen languages before 1914 and became the accepted popular summation of Marxist theory. This document came to define 'orthodox' socialist theory before the October Revolution of 1917 caused a major split in the international socialist movement.