Informal Diplomacy and Transnational Networks between the Spanish Partido Socialista Del Interior and the Socialist International (1969–74)

This article examines the underexplored role of the Spanish Socialist Party of the Interior (PSI), later the Popular Socialist Party (PSP), in the transnational struggle against Francoism and the democratisation of Spain. Moving beyond the dominant historiographical focus on the Spanish Socialist Workers’ Party, it investigates how the PSI–PSP forged a robust international network – particularly with the Socialist International (SI) – through a distinct strategy of informal diplomacy. The study’s central aim is to highlight the originality and effectiveness of the PSI–PSP’s communicative tactics, which blended official channels with informal, academic and personal connections, in navigating Cold War–era political dynamics. Anchored in the conceptual frameworks of informal diplomacy, multi-track diplomacy and new diplomatic history, the article situates the PSI–PSP’s initiatives within broader debates on soft power and the role of non-state actors in international relations. Methodologically, it relies on a wide range of primary sources, including unpublished internal documents from the personal archive of the former secretary general of the party, international archives and oral history interviews with former PSI–PSP members. Press sources are also utilised to triangulate key events and statements. The article aims to demonstrate that while the PSI–PSP ultimately failed to gain formal recognition from the SI, its informal diplomatic practices yielded significant symbolic and practical outcomes. It concludes by arguing for a reconceptualisation of transnational socialist networks, emphasising the indispensable role of informal relations in shaping the institutional and political architecture of European social democracy during Spain’s transition to democracy.