In 1876 he returned to France to become one of the chief French apostles of Marxian collectivism, and was imprisoned for six months in 1878 for taking part in the first Parisian International Congress.
Next year at the Reims congress the orthodox Marxian programme of Guesde was opposed by the "possibilists," who rejected the intransigeant attitude of Guesde for the opportunist policy of Benoit Malon.
If he did not always find it easy in his later years to follow the new developments, he preserved to his death the idealism of his youth, the hatred both of Liberalism and of State Socialism; and though he was to some extent overshadowed by Bebel's greater oratorical power, he was the chief support of the orthodox Marxian tradition.
In both Weberian and Marxian traditions conflict was recognized as central to industrial society.
During their long sojourn in London, Engels assisted them to acquire the Marxian method.