AbstractThis paper revisits and rebuts the mainstream view that Brazil and Argentina were led to form the Southern Common Market to end more than a century of rivalry and competition. We find the elements characterizing an interstate rivalry diminishing in the nineteenth century through the promotion of peaceful settlements and strategic alliances while those that could prompt security concerns disappeared years before the Southern Common Market was formed. Except for diplomatic disputes over the distribution of shared water resources, a disagreement settled in 1979, the decades preceding the Treaty of Asuncion were typified by security alliances, co-operation on economic complementarity and the promotion of bilateral institutions. We find little evidence for the implied security motivations being proposed in the literature. Rather, the establishment of the Southern Common Market was driven primarily by Argentina's and Brazil's desire to improve economic performance and advance political leverage through the promotion of a common stance in global affairs. This view challenges a common component in integration theory that, as applied to the European Union and elsewhere, asserts the privileged role of security concerns as prime driver for integration. This matters because there is a misapprehension that affects both the theory about integration as well as the formulation of policy prescriptions for South America.