George Orwell's 'Homage to Catalonia' is an important historical first hand account of the confusion and treachery as well as bravery and privation of participants in the Spanish Civil War, as well as the long suffering citizens of Spain.
The book could do with a glossary, but don't be put off by all the acronyms for the many factions involved in the conflict.
Catalonia and its capital Barcelona was a hot bed of anarchism and revolution by the workers and peasants against the ruling classes and the Catholic Church, precipitating the Civil War which started in Barcelona and ran from 21 July 1936 to February 1939, during which time Spain was divided between the Socialist Republican Government supported by various Socialist and Anarchist factions initially controlled much of the east and southern Spain, and the Fascist Nationalist Government under Franco, controlled much of western and central Spain, gradually whittling away most of the Republican controlled area.
George Orwell rather by chance joined the POUM militia (Partido Obrero de Unificación Marxista) the Workers party of Marxist Unification - supported by Trotskyists and the workers and peasants bloc.
Other revolutionary political factions included the FAI or Iberian Anarchist Federation (Federación Anarquista Ibérica); The Stalinist Unified Socialist Party of Catalonia PSUC (Partit Socialista Unificat de Catalunya), which did everything to frustrate its Trotskyist rival POUM including diverting arms from the POUM militia at the front.
Most international volunteers (including my great-uncle Tom Bailey from Canada) joined the International Brigades that were set up by the Communist International which was very active in many countries during Stalin's time (In most countries it was actually illegal to join the IB, with members risking imprisonment on their return home). Whilst the IB was much better resourced than POUM, it was equally unsuccessful in defeating the Franco Nationalists (Fascists).
George Orwell's experiences in Spain from December 1936 to June 1937 included 2 tours of duty totaling 115 days fighting with POUM on the front at Aragon, culminating in his being seriously wounded in the neck; with periods of R&R in Barcelona with his wife Eileen. In May 1937 during George's leave was interrupted when the Republican Government suddenly moved to exert control over the revolutionary factions in Barcelona culminating in POUM being declared illegal on 16 June 1937, forcing George and Eileen to flee to France.
Unfortunately because the support of Stalinist Russia was essential to survival of the Spanish Republican Government, the so called 'united' front against the Fascists was somewhat less than united, and ultimately failed to stem the advance of the Franco forces which were supported by the Italian and German air forces and naval bombardment of strategic positions, as well as enjoying the support of the Spanish middle classes, the Catholic Church, and the acquiescence of Western democracies.