The arrangements between Brazil and Argentina that turned ''rivals into friends'', and which allowed for policy coordination in the nuclear realm are commonly regarded as a result of presidential diplomacy carried out by civilian presidents José Sarney and Raúl Alfonsín in the 1980s. In that sense, the Iguazu Declaration (1985) is traditionally regarded as a turning point in the relationship between the two countries. The goal of this article is three-fold: first, it investigates whether Sarney-Alfonsín efforts, as well as the transition to democratic regimes actually account for foreign policy change (dependent variable) in the region. Second, it tests the hypothesis that a new paradigm was only established in the 1990s, under Carlos Menem and Fernando Collor administrations. Last, it analyzes Brazil and Argentina’s foreign policy under a comparative perspective in order to identify and assess factors that have proved critical in each case. This work adopts a historical institutionalist and considers both domestic as well as international factors as independent variables. Empirical data stem from Brazilian and Argentine historical archives, recently declassified documents, press records and oral history interviews with diplomats, political leaders and technicians involved in nuclear activities in the region and elsewhere.
