This thesis investigates the pivotal shift in U.S. foreign policy during the mid-to-late Cold War, specifically examining the transition from aggressive anticommunist containment to a framework prioritizing human rights. Focusing on the military-led regimes of Uruguay and Argentina, it argues that these two nations served as case studies for the first major revisions of American policy on humanitarian grounds. While the Kennedy, Nixon, and Ford administrations historically utilized Cold War imperatives to justify supporting repressive right-wing governments, the mid-1970s saw the emergence of a new political process. Driven in part by the advocacy of NGOs like Amnesty International and the legislative leadership of figures such as Congressman Donald Fraser (DFL-MN), human rights evolved from abstract idealism to concrete policy prescriptions. This research highlights the landmark decisions to revoke military aid to Uruguay in 1976 and Argentina in 1977, illustrating how a burgeoning network of activists, academics, and policymakers successfully challenged establishment foreign policy views. By analyzing these two Southern Cone countries, the thesis explores how the brutality of such civic-military dictatorships were catalysts for change. The U.S. decision to ban military aid to those governments marks a true inflection point not because it set the United States on an entirely different path, but because it allows us to examine what different policy choices were possible, despite all the constraints of that era.