This thesis focuses on the practice of cultural diplomacy in post-imperial contexts through the study of the Spanish-Latin American case (Hispano-Americanism) during the 1920s. It advances the concept of ‘spiritual empire’ to make sense of the weight of imperial legacies in multilateral international relations. It highlights the intangible and imagined nature of these legacies, and examines their use in foreign policy. It thus offers broader definitions of what is usually called ‘soft power’, with a specific emphasis on its European roots and on its intertwinement with empire and multilateralism during the interwar period, especially in the context of the League of Nations. The specific object of this inquiry is the set of practices of Hispano-Americanism developed under General Miguel Primo de Rivera’s authoritarian regime (1923-1930). Calls for closer relations between Spain and the Spanish-speaking American countries dated back to the late nineteenth century, in the form of intellectual pleas and some political projects. Only in the 1920s, however, was Hispano-Americanism built up as a relatively coherent set of diplomatic practices. Asking why these practices emerged in the 1920s in particular, the thesis explores this decade as a key moment for both empire and diplomacy. Building mostly on archival material from the Spanish administration, the League of Nations, and US public and private institutions, this research inserts Spanish diplomacy at the heart of the narrative of power politics in Europe and the Americas. The aim is not to prove that Spain actually mattered, but to use this specific case study to pose alternative questions about power in world politics. Rather than asking where power is, this thesis seeks to understand what power is and how it is fabricated. The notion of spiritual empire illustrates how the imperial logics of power resist the formal end of empires and are reused in the shape of diplomatic and administrative practices. It explains how Spanish diplomats and foreign-policy makers tried to hang on to a status of power granted by Spain’s imperial past. It also opens the way to diachronic comparisons between Spain’s Hispano-Americanism, Portugal’s politics of Lusophony, France’s politics of Francophony, or the British Commonwealth, among others.