The Workers' Party of Marxist Unification (POUM, Partido Obrero de Unificación Marxista) was a Spanish political party around the time of the Spanish Civil War. The party was formed by the fusion of the Trotskyist Left Communists of Spain (ICE) and the Workers and Peasants Bloc (BOC) against the will of Leon Trotsky with whom the former broke. They were formed as a Communist party in opposition to Stalinism in 1935 by Andres Nin and Joaquin Maurin. They were heavily influenced by the thinking of Leon Trotsky, in particular his Permanent Revolution thesis.
They were larger than the official Communist party in Catalonia and Valencia and highly critical of the Popular Front strategy. But did take part in the Spanish Popular Front initiated by the leader of Acción Republicana, Manuel Azaña. The POUM tried to see through 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.
During the Spanish Civil War the party began to grow in popularity and alongside the anarchist National Confederation of Workers (CNT) commanded the support of most of the proletariat in the zone not controlled by the fascists during the war. The British author George Orwell, a member of the Independent Labour Party fought alongside POUM forces in the civil war.
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 itself in actual fighting between their supporters.
These divisions between the forces supporting the Popular Front allegedly aided Francisco Franco in winning the civil war.