Historians have struggled to define the evangelical consensus that dominated American life for most of the nineteenth century. Scholars of the antebellum church tend to emphasize how it exacerbated sectional tension and precipitated the Civil War, while scholars of the postbellum church emphasize how it bolstered sectional reunion. But how can both have been true? I address this question by examining one denomination, the bulk of whose membership lived in the trans-Appalachian South and the lower Midwest. Focusing on one denomination averts the shortcomings of studying American evangelicalism as a homogenous whole when it was no such thing. Moreover, the Cumberland Presbyterian Church, because it was arguably the largest denomination not to divide along sectional lines during the Civil War era, allows us to locate important continuities across time (before and after the war) and space (north and south of the Mason-Dixon line).

And what do I find? That the heart of the evangelical consensus was the project of the Christian nation—the belief that America had a special mission to purify the church and evangelize the globe. At least for the Cumberland Presbyterians, Christian nationalism was a useful tool in addressing the two great problems that a Protestant denomination faced in the nineteenth-century United States: namely, the religious marketplace and the institution of slavery. But at the same time, those two same forces actually undercut the Cumberland Presbyterian narrative of the Christian nation. This paradox helps explain how Christian nationalism, and by extension the evangelical consensus, could both reinforce and undermine the union of the republic.