The Division of Labor and the Creation of Overlapping Security Institutions: Evidence from South America

Why do states create overlapping regional security institutions? Existing explanations argue that states build overlaps to gain strategic leverage. However, recent scholarship shows that overlaps also tend to create functional differentiation. We bridge these two strands by arguing that an anticipated division of labor can motivate institutional overlap creation. Some states seek a new organization to supply governance tasks that the existing ones cannot provide, and this task-driven innovation combines with strategic-leverage motives within heterogeneous founding coalitions. We test the argument by examining the overlap between the Union of South American Nations/South American Defense Council (UNASUR/SDC) and the Organization of American States (OAS) in South American security governance. Our set-theoretic analysis shows that strategic-leverage accounts are insufficient to explain the UNASUR/OAS overlap. Then, a within-case analysis shows that the demand for routine defense interactions and defense-industrial coordination—tasks not provided by the OAS—completed the combination of conditions that produced the overlap. The findings link theories of overlap creation and overlap ordering, and identify conditions under which institutional overlap in security governance is designed to be complementary rather than purely competitive across regions and issue contexts.