Is it domestic politics or the international system that more decisively influences foreign policy? This article focuses on Latin America's three largest powers to identify patterns and compare outcomes in their relations with the regional hegemon, the United States. Through a statistical analysis of voting behavior in the UN General Assembly, we examine systemic variables (both realist and liberal) and domestic variables (institutional, ideological, and bureaucratic) to determine their relative weights between 1946 and 2008. The study includes 4,900 votes, the tabulation of 1,500 ministers according to their ideological persuasion, all annual trade entries, and an assessment of the political strength of presidents, cabinets, and parties per year. The findings show that while Argentina's voting behavior has been determined mostly by domestic factors and Mexico's by realist systemic ones, Brazil's has a more complex blend of determinants, but also with a prevalence of realist systemic variables.T he emergence of left-leaning governments throughout Latin America, the socalled Pink Tide, has become conspicuous in recent years. As a consequence of the pervading ideology of the new administrations, "one would expect a more assertive approach to foreign policy" (Gardini and Lambert 2011, 1). This scenario provides a good opportunity to perform a test: to evaluate the relative weights of systemic and domestic variables. Since the United States has been traditionally the antimodel and antagonist for the Latin American left-as much as a reference and ally for the right-we posit that focusing on a country's alignment with the United States is a proper way to gauge the impact of ideology and related domestic factors, such as regime type, on foreign policy. From a more general perspective, this strategy can inform us as to whether it is systemic or domestic forces that have more decisively influenced Latin American foreign policy.