William Wilberforce and his coterie of evangelical activists have regularly attracted research. Attention, however, has focused almost exclusively on the group's efforts in Britain, with little scholarly work to date on its connections and trajectories overseas. This article examines the influence of Clapham thought and activity in the early American republic. By tracing transatlantic correspondence and reconstructing international relationships, it unveils the direct influence of Clapham theological understandings, notably in their challenge to received interpretations of racial inequality and competing national virtues. Less directly, as Clapham principles shaped Britain's policing of the seas and became enacted in diplomatic decisions, British moralism created friction and resentment with the U.S. government. Although the threads of overt ideological influence by the Clapham Sect appear thin with respect to antislavery, more nuanced influences in terms of race, theology, and empire reveal profound contextual challenges. Yet, the factors limiting the Clapham Sect's impact are as instructive as the influences because they illuminate the contrasts across the Atlantic, which turn out in this case to be more important than the continuities. Transnational approaches to history have often erred by overlooking the transformation of religious and moral ideas across borders, leaving our understanding of transatlantic abolitionism theologically impoverished. By situating Britain's most famous abolitionist group in a wider context, this article exposes the neglected role of race and competing moralities in nineteenth-century international religious history, confounding notions of simple transference of ideas and intellectual continuity across the Atlantic.