Borderland regions in Southeast Asia have increasingly been reimagined as resource-rich, unexploited ‘wastelands’ targeted for large-scale development schemes for economic integration and control. Common and overlapping features of these regions are processes of resource extraction, agricultural expansion, population resettlement, and securitization, and the confluence of these dynamic processes creates special frontier constellations. Through the case of the Indonesian-Malaysian borderlands, I explore how processes of frontier colonization through agricultural expansion have been a recurrent product of Indonesian development and security policies since the early 1960s. I argue that frontier development accelerates and intensifies when national discourses of security and sovereignty and state-led agrarian expansion intersect along national borders. The study generates new insights into how contemporary state-capitalist processes of agricultural expansion in the borderlands of Indonesia and other parts of Southeast Asia are justified through discourses of national sovereignty and notions of ‘untamed’ and ‘wild’ resource frontiers. I highlight the multiple meanings and notions associated with regions where resource frontiers and national borders interlock. The study offers an explanation of how frontiers as discursive constructs and material realities play out along national borders.