<p>This article develops a theory of comparative state formation and state building that accounts for the distinctive pattern of nineteenth century political development in the United States. The theory builds on the distinction between the pioneer states of Western Europe and the latecomer states of Latin America. Whereas state formation—the process of territorial consolidation—went hand in hand with state building and the development of administrative capacity in Western Europe, state building was decoupled from state formation in Latin America. These divergent experiences reflect core features of the international system that prevailed during periods of political development: anarchic and feudal conditions produced “war-led” state formation in Early Modern Europe, while geopolitical hierarchy and global capitalism generated “trade-led” state formation in Latin America. This international context is critical for understanding the United States in comparative perspective. We highlight two overlooked features of the United States during its formative period of political development (roughly the 1750s to the onset of the U.S. Civil War). First, the international context combined elements of both war-led and trade-led paths—sharing partial commonalities and differences with European pioneers (geopolitical uncertainty and territorial pressures) and Latin American latecomers (capitalist integration under emerging hierarchy). Second, this period of political development straddled a fundamental shift in the international system: the end of the Napoleonic Wars and the subsequent consolidation of Pax Britannica after 1815 marked a transition from anarchy to hierarchy and intensifying global commerce. We argue that this mixed and temporally evolving international context set the United States on a distinctive developmental path that departed from European patterns while overcoming some of the state-building impediments characteristic of latecomer states in Latin America.</p>