The "South American Great Lakes System" (SAGLS) project was an unimplemented geographical and environmental engineering project of the 1960s, originally envisioned to "improve" the environmental, economic, social, cultural, and political landscapes of South America by transforming the Amazon and other mayor rivers into a series of massive interconnected lakes. I investigate, why this geo-engineering was promoted, by whom and what it meant for its organizers and opponents. I argue that the SAGLS's transnational network of promoters envisioned this geo-engineering project as an effective modernization strategy and as an infrastructural-technological solution to the problems of underdevelopment and political unrest. For close to a decade the SAGLS project circulated among technocratic elites in both North and South America, who considered it as an appropriate strategy for modernization and counter-insurgency. I examine their justifications of the project; the private, public and multilateral institutions they lobbied to endorse it; and the dissenting voices opposing or criticizing the scheme. Analyzing previously unexamined archival materials, including cartographic documents, I investigate how this transnational network of modernizers sought to incorporate "the underdeveloped tropical landscapes and insurgent populations" of South America into "the maps of capitalist modernization." In the process, I pay special attention to ideas of tropical nature, poverty and underdevelopment, generated to support —or dispute—this geo-engineering project. By studying projects like SAGLS, I suggest that we re-evaluate traditional interpretations of modernization, technology and counter-insurgency. Specifically, by unearthing the cartographies of the SAGLS and mapping the transnational network that advanced the SAGLS project, my dissertation reexamines U.S. and Latin American relations to de-center the Cold War's traditional US-centric narrative defining North-South relationships.