Unión General de Trabajadores in the context of "Labor movement in Spain"

The Popular Front (Spanish: Frente Popular) was an electoral alliance and pact formed in January 1936 to contest that year's general election by various left-wing political organizations during the Second Spanish Republic. The alliance was led by Manuel Azaña. In Catalonia and the modern-day Valencian Community, the coalition was known as the Front of the Lefts (Catalan: Front d'Esquerres).

The Popular Front included the Spanish Socialist Workers' Party (PSOE), Communist Party of Spain (PCE), and the republicans: Republican Left (IR), (led by Azaña) and Republican Union (UR), led by Diego Martínez Barrio. This pact was supported by Galician (PG) and Catalan nationalists (ERC), the POUM, socialist union Workers' General Union (UGT), and the anarchist trade union, the Confederación Nacional del Trabajo (CNT). Many anarchists who would later fight alongside Popular Front forces during the Spanish Civil War did not support them in the election, urging abstention instead.

The phrase Spanish Republic at war refers to the Second Spanish Republic during the Civil War of 1936–1939. It represents the last stage in this war's history. The territory that remained under its control after the coup of July 1936—which was called the republican zone or the loyalist zone—gradually reduced as the rebel zone spread, until it was finally occupied in its entirety by the Francoist side (which had referred to the areas as the red zone throughout the civil war).

During this time, there were three consecutive governments: the one presided over by José Giral, from Republican Left, although during his short term (July–September 1936), real power was actually in the hands of the hundreds of committees that were created when the social revolution of 1936 broke out. The next government was presided over by Francisco Largo Caballero, the leader of the Spanish Socialist Workers' Party (PSOE) and the Unión General de Trabajadores (UGT), one of the two trade unions that had led the revolution. Finally, the third government was presided over by Juan Negrín, also from the PSOE, as a consequence of the fall of Largo Caballero's government after the events of May 1937. Negrín governed until early March 1939, when Colonel Segismundo Casado's coup took place, putting an end to the Republican resistance and giving way to the victory of the rebel faction led by General Francisco Franco.

Revolutionary Catalonia (21 July 1936 – 8 May 1937) was the period in which the autonomous region of Catalonia in northeast Spain was controlled or largely influenced by various anarchist, syndicalist, communist, and socialist trade unions, parties, and militias of the Spanish Civil War era. Although the constitutional Catalan institution of self-government, the Generalitat of Catalonia (led by the Republican Left of Catalonia, ERC), remained in power and even took control of most of the competences of the Spanish central government in its territory, the trade unions were de facto in command of most of the economy and military forces, which includes the Confederación Nacional del Trabajo (CNT, National Confederation of Labor) which was the dominant labor union at the time and the closely associated Federación Anarquista Ibérica (FAI, Iberian Anarchist Federation). The Unión General de Trabajadores (UGT, General Worker's Union), the POUM (Workers' Party of Marxist Unification) and the Unified Socialist Party of Catalonia (PSUC, which included the former Communist Party of Catalonia) were also prominent.

Socialist rule of the region began with the Spanish Revolution of 1936, resulting in workers' control of businesses and factories, collective farming in most of the countryside, and attacks against Spanish nationalists and the Catholic clergy. The growing influence of the Communist Party of Spain (PCE) in the Popular Front government and their desire to nationalize revolutionary committees and militias brought it into conflict with the CNT and POUM, resulting in the May Days and the eventual replacement of the CNT by the PSUC as a major political force in Catalonia until their defeat to the Nationalist forces in 1939.

The Spanish Syndical Organization (Spanish: Organización Sindical Española; OSE), popularly known in Spain as the Sindicato Vertical (the "Vertical Trade Union"), was the sole legal trade union for most of the Francoist dictatorship. A public-law entity created in 1940 and defined as subordinate to the ruling party FET y de las JONS, the vertically-structured OSE was a core part of the project for frameworking the Economy and the State in Francoist Spain, following the trend of the new type of "harmonicist" and corporatist understanding of labour relations vouching for worker–employer collaboration developed in totalitarian regimes such as those of Nazi Germany and Fascist Italy in the first half of the 20th century. Up until the early 1950s, it internally worked—at least on a rhetorical basis—according to the discourse of national syndicalism. Previous unions, like the anarchist CNT and the socialist UGT, were outlawed and driven underground, and joining the OSE was mandatory for all employed citizens. It was disbanded in 1977.