Some were involved in the fighting in Barcelona against Republican opponents of the Communists: the Workers' Party of Marxist Unification (POUM) (Partido Obrero de Unificación Marxista, an anti-Stalinist Marxist party) and anarchists.
Nogen var involveret i kampen i Barcelona mod republikanere, som var modstandere af kommunisterne: POUM Partido Obrero de Unificación Marxista, et anti-stalinistisk marxistisk parti og anarkister.