Pan-Americanism’s promotion of liberal internationalism and pan-Africanism’s appeals to transnational solidarity among African people(s) provided useful frames for critics of non-interference to make it the subject of debate. I argue that the content and political salience of pan-Americanism & pan-Africanism empowered – or even inspired – critics of non-interference in these regions. In this chapter I offer a long-term account of the (uneven) erosion of non-interference at the regional level in the global South, an account centering on the contestedness of this norm within the OAS and OAU compared to ASEAN during the Cold War period. This contestation (at the level of discourse) contributed over time to norm erosion (at the level of law and practice). Pan-Asianism did not serve the same function. Since non-interference was less contested in Southeast Asia (and not on these grounds), it was therefore more robust or resilient over time. Because of the history of norm contestation and erosion, the three regional groupings arrived at the 1980s with different normative priors. This meant that Latin America and Africa were more amenable to the intrusive regionalism trend than was Southeast Asia.