Fit Instruments: Gaels, Indians, and the Diverse Origins of Imperial Reform and Revolution compares the experiences of three groups of marginalized people in the eighteenth century British empire—Native Americans, Irish Gaels, and Scottish Gaels—in order to better understand race and exclusion in early America. Drawing on Native American council speeches as well as Gaelic-language poetry, I argue that these marginalized people strove to reshape empire in ways that reflected their cultural and material interests, ensuring that questions of diversity drove the process of imperial reform and revolution. I argue that the American Revolution—and its troubling racial legacies—must be understood as a response, one among many, to that imperial reality and the difficult global transition from empire to nation-state.Fit Instruments begins with the Glorious Revolution of 1688-90, describing how the late seventeenth century witnessed the creation of tentative alliances between the empire's indigenous peoples and the Crown—as well as the ways that Anglophone provincials used these alliances as a justification for ousting James II, creating an "exclusionary constitution" that barred indigenous people from the benefits of empire. This constitution began to crumble in the 1740s, when Gaelic and Indian people forced themselves onto the imperial agenda in a series of events that convinced imperial leaders that winning over indigenous people would be central to victory in the imperial struggle against France.This "Atlantic' 45," I argue, reveals that imperial reform had different origins and goals than is usually assumed: it was focused on the need to manage diversity within a broader imperial framework. The second half of the project tells the story of successive imperial attempts to do so, with emphasis on the ways that Gaelic and Indian people themselves contributed to imperial reform both as its targets and as active participants. Fit Instruments closes with an epilogue that depicts the American Revolution as one possible response to these changing imperial understandings of diversity, arguing that the familiar American struggle with race and exclusion owes much to its roots in an imperial crisis fundamentally concerned with the role of government in managing diversity.