Thanks to the mediation of the Austrian anarchist Max Nettlau, many Spanish and Italian archives were channeled to the IISH. This inveterate collector was close friends with several Spanish anarchists such as Diego Abad de Santillán and Federica Montseny, and with Italians such as Luigi Fabbri and Ugo Fedeli. During the 1920s and 1930s, Nettlau frequented Spain, As did Arthur Lehning, the new head of the Anarchism and Latin department of the IISH. The anarchist collections gathered by Nettlau arrived at the Institute at the end of 1935, which made it the most important repository of anarchist records and papers in the world.
When the defeat of the Republicans was immanent in the summer of 1938, a prominent member of the Federación Anarquista Ibérica (FAI), Diego Abad de Santillán, contacted the IISH to find a safe haven for various archives of the Left. After being miraculously smuggled across the border shortly before Catalonia fell, the "Spanish boxes" (as they came to be known) reached the IISH Paris branch. They contained the archives of the Federación Anarquista Ibérica and the Confederación Nacional del Trabajo (CNT). In the postwar years, the majority of the Spanish archives obtained by the Institute bear the hallmark of the Civil War and of Anarchism. The archives of exiled anarchists and organizations in exile, including Fernando Gómez Peláez, José Martinez Guerricabeitia and his publishing house Ruedo Ibérico, and the Federación Española de Deportados e Internados Politicos (FEDIP) are outstanding examples. Other interesting collections arrived because of the historians who researched the subject, including a vast collection on the Comissiones Obreras CCOO in the 1960s and 1970s. These workers' committees were set up in large industrial settlements to fight for the rights of workers and improve the low salaries, a task neglected by the official trade unions. The Committees operated within the boundaries of legality.
Like the Spanish archives, the Italian archives at the IISH bear the hallmark of anarchism. Clear examples of this are the archives of Armando Borghi, which include many documents on Errico Malatesta, the archives of Ugo Fedeli, and Luce Fabbri and her father Luigi Fabbri. The archive of the Partito Anarchico Italiano chronicles the anarchist movement of the 1980s and 1990s. The papers of the socialist leader Filippo Turati are a notable exception. The Institute acquired these documents with the help of Julius Braunthal (the secretary of the Socialist International and one of our board members) in 1956. Turati maintained a lively correspondence with a wide range of people in and outside the Second International, from Friedrich Engels to Benoît Malon.