The article analyses the approach to external affairs adopted by Spain's Union General de Trabajadores (UGT) during the interwar period, within the proletarian internationalist framework. The documents consulted are from the International Institute of Social History in Amsterdam, the Francisco Largo Caballero Foundation and the Pablo Iglesias Foundation. A large number newspaper archives were also examined. Documents on external affairs produced by the Internationals and the Spanish Trade Union Confederation are compared methodologically. The period between 1919 and the outbreak of the Spanish Civil War saw the stabilization of the international labour landscape. UGT leaders were convinced that internationalism was the best way to solve major problems. Events showed workers' organizations to be powerless to face the major challenges arising in the Twenties and Thirties. UGT looked to internationalism to justify the reformist strategy it had adopted at home. During the Black Biennium, it contributed to the radicalization of leaders and activists. The article seeks to show that external policy was very influential on the strategic line adopted by the Union inside Spain throughout this time.
unionism; Union General de Trabajadores (UGT); internationalism; interwar period; IFTU; ILO