It has recently been suggested that the economic departure of the United States after the Civil War marked a "Second Great Divergence". Compared to the "First", the rise of Britain during the Industrial Revolution, this Second Great Divergence is curiously little understood: because the United States remains the template for modernization narratives, its trajectory is more easily accepted as preordained than interrogated as an unlikely historical outcome. But why should development have been problematic everywhere but in the United States? This Viewpoint argues that a robust explanation for the United States' rise is lacking: it can neither be found in an economic history literature focused on factor endowments nor in internalist Americanist historiography, which often reproduces overdetermined accounts of modernization inspired by Max Weber. The most promising avenue of inquiry, we argue, lies in asking how American political institutions configured what should properly be called an American developmental state. Such a perspective opens up a broad comparative research agenda that provincializes the United States from the perspective of development experiences elsewhere.