This dissertation is a history of nineteenth-century state formation in regions of transnational mobility. Recently, historians have rejected the teleological structuralism of past scholarship for narratives of contingency and bottom-up agency in understanding post-independence state formation in Latin America. However, they have been unable to balance individual agency and global economic structures, leaving underexplained the connection between bottom-up state formation and the rise of global capitalism. To connect these processes, this dissertation examines a mountainous region (or the Transandean) between Argentina and Chile, and its transition from a place of warfare to one of infrastructure by examining the movement and circulation of people and things in it. To that end, this dissertation begins with the Transandean’s emergence in the mid-nineteenth century as a space of commerce, labor migration, transportation, and itinerancy. The uncertainties underpinning Transandean mobility fueled the civil conflicts that defined mid-century nation-state formation in Argentina. To create economic and political stability, state and capital embarked on a project of infrastructural development, necessitating an engineering class to manage it. In the process, engineers reframed the relationship between state and capital, rationalizing and solidifying the liberal state and capitalist order by the end of the century.