We should theorize about international relations (IR) exclusively on the basis of systemic variables because the whole cannot be known 'through the study of its parts'. This injunction is familiar and pervasive across our discipline. Yet, IR theorists who seek to explain international outcomes by focusing exclusively on systemic variables are increasingly engaging in a sort of unilateral disarmament. Despite all its shortcomings, foreign policy analysis (FPA) gets us much further than systemic IR theory in understanding the real world of international politics. While much depends on precisely what 'slice' of international political life we are seeking to explain, FPA captures how international outcomes are increasingly determined by factors that are sourced at the level of domestic politics. The argument here draws on close empirical investigation of US-European relations, as well as contributions to this journal by Mearsheimer and Gilpin, and other recent works in the research literature.