They fought for the Republicans during the Spanish Civil War. The POUM differed from the Russian communists and opposed Stalin. George Orwell signed up to fight for the POUM, considering it the local version of the Independent Labour Party.
In Barcelona, the POUM were involved in street fighting against the pro-Stalin communists. Fitz Kreiner fought alongside Joaquín — a POUM member — in the fighting. After the fighting subsided, the POUM were accused of inciting violence among the Republican forces in an attempt to aid Nationalist forces. (PROSE: History 101)