Weaponizing Geography demonstrates the consequences of unbuilt mega-projects. It tells the untold story of how a series of high modernist Cold War projects came into being and what their proponents hoped to achieve, as well as the successes, failures, and consequences of their actions. It examines the so-called “South American Great Lakes System” (SAGLS), a geographical and environmental engineering project (1964-1973) proposed by the Hudson Institute of New York, a think tank related to the U.S. Department of Defense. With the support of influential Latin American elite members, engineers, and war strategists at this think tank sought to transform the major rivers of the continent into a series of massive interlocked, channelized, and navigable artificial reservoirs. Much like the North American Great Lakes, these waterways would provide (in theory) inexpensive riverine transportation, inexhaustible sources of hydropower, and a landscape facilitating large-scale agroindustry, mining, and counterinsurgency operations in allegedly “unexploited and unexplored” tropical regions.Weaponizing Geography focuses largely on the Chocó Development Project (CDP), a SAGLS prototype plan embraced by the Colombian government to build a pair of interconnected and power-generating artificial reservoirs in the northwestern region of this country: a strategic area bordering Panama, inhabited by disregarded indigenous and afro-descendent populations, where the SAGLS idea could be tested to deliver a low-cost interoceanic passage alternative to the Panama Canal, purportedly accomplishing nineteenth-century visions for a modern canal connecting the Atrato and San Juan rivers in Chocó. So even if —retrospectively—we now know that the most visible components of SAGLS and CDP project were never implemented, it is key to understand that for close to a decade they did exist as a conceivable strategy for modernization and securitization, performing different kinds of work for different historical actors, with specific influences and consequences (including material and territorial effects.) Following the trajectories and afterlives of these mega-projects, this dissertation illuminates intersecting histories of technology, environment, and geopolitics, offering new perspectives on Latin American–U.S. relationships during the Cold War. In doing so, it also contributes to recent scholarship in cartographic, agrarian, development, infrastructure, and counterinsurgency studies.