<p>This article examines Immanuel Wallerstein’s intellectual evolution during his first decade at Columbia University, tracing his shift from a politically engaged but methodologically conventional undergraduate to a radical thinker increasingly disillusioned with mainstream American social science. At the center of this transformation was C. Wright Mills, his teacher and informal mentor, whose critical sociology provided both inspiration and a foil. Though Wallerstein moved beyond Mills in many respects, he nonetheless advanced elements of Mills’s project, above all by realizing the call to reunite sociology with history—an emphasis that would later converge with the emergence of world-systems analysis. This trajectory unfolded amid a broader crisis in postwar social science, as Cold War liberalism and empiricist orthodoxy faced mounting challenges from critiques of capitalism, imperialism, and Eurocentrism. Columbia served as a microcosm of these tensions: the quantitative rigor of Paul Lazarsfeld’s Bureau of Applied Social Research stood alongside the heterodox interventions of Mills, Karl Polanyi, and émigré critical theorists. Wallerstein’s experience in this milieu, marked by institutional privilege and political friction, proved decisive for his intellectual path and offers a lens onto the development of American sociology in the early Cold War era.</p>