The South American Defense Council (SADC) aimed to coordinate regional defense policies and build confidence among its members. It diffused practices among its members, such as a standard methodology to report defense expenditures. However, we still need a proper understanding of how it happen. In this article, I contribute to understanding defense cooperation in South America by answering which mechanisms allowed the Council to diffuse policies. Using evidence from the Council’s meeting records and process tracing, I show that SADC boosted interactions and set and monitored the implementation of particular practices on defense policies.