[2] Rosmer was a syndicalist leader before World War I, active in the Confédération générale du travail (CGT), the French general federation of unions.
Together with Pierre Monatte, he issued a journal called La Vie ouvrière (Worker's Life), which was terminated as a result of French entry into World War I.
[3] The antiwar French syndicalists had been represented at the Zimmerwald Conference in 1915 and then organised as the Committee for the Resumption of International Relations in which Rosmer participated.
[2] After his expulsion from the PCF, Rosmer helped found the journal La Révolutuion prolétarienne (The Proletarian Revolution) and participated in political activities in a circle organised around this magazine.
[6] Unable to return to France because of the outbreak of World War II, Rosmer, an American by birth, lived in the United States after his Mexican interlude.