They were larger than the official Communist party in Catalonia and Valencia and highly critical of the Popular Front strategy, but they did take part in the Spanish Popular Front initiated by the leader of Acción Republicana, Manuel Azaña. The POUM tried to implement some of its radical policies as part of the Popular Front government but these were resisted by the more moderate factions. This political disagreement would cause Nin to leave the government.
The POUM's support of Trotsky and opposition to Josef Stalin caused huge ruptures between them and the Communist Party of Spain, still unswervingly loyal to the Third International. These divisions manifested themselves in actual fighting between their supporters.
These divisions between the forces supporting the Popular Front allegedly aided Francisco Franco in winning the civil war.
External link
The Fundación Andreu Nin (http://www.geocities.com/CapitolHill/9444) has a Spanish-language site containing an extensive collection of documents, biographical notes, and links related to the POUM.
But as the POUM continually pointed out, recognition of the need for an electoral agreement with the left wing Republicans to defeat the right at the polls was not the same thing as political capitulation to the petit-bourgeoisie.
The POUM stressed that the success of the left was neither a victory for bourgeois democracy, nor did it represent mass support for petit-bourgeois Republicanism, but was a by-product of the revolutionary struggle of October 1934.
The POUM unceasingly denounced the attempts of the Stalinists and the Social Democrats to subordinate the workers’ movement to petit-bourgeois Republicanism.
The POUM (Workers Party of Marxist Unification) was formed on 29 September 1935 at a meeting of the leaders of the BOC and the ICE.
What can be discounted is the view that the POUM was simply the continuation of the BOC under a different name, and that Maurín had agreed to the fusion of the two organisations solely with the intention of strengthening his party’s leadership with the incorporation of the talented Nin.
It is worth noting that at least some POUM leaders became extremely critical of the London Bureau during the Civil War, but the subsequent repression of the party prevented this criticism from developing further and into an open split.