A stronghold for anarchists...until the Communists started murdering the anarchists.
There were several groups. Even Orwell while fighting with other foreign socialists for the `Republic’ had trouble keeping them straight. Some of his experiences there led to his disenchantment with communist ideals v. reality, leading to Animal Farm, then 1984.
His book Homage to Catalonia, for anyone interested. He was wounded in the throat and got the hell out of Dodge.