This thesis proposes an engagement with International Relations from the perspective of 19th Century Atlantic slavery by looking to Brazilian and US archives that date from the 1800s. The argument developed in the following pages is centered on the possibility of articulating forms of belonging not defined in spatial terms. Developing a political thought premised on 19th Century Atlantic Slavery is a way of focusing on the political phenomenon without conditioning it to the state spaciality. This emphasis on the politics, instead of on the spatiality, allows for considering new ways of belonging and new approaches to the delimitation of space. In this thesis I develop them by proposing a debate on the concept of Empire. In characterizing Slavery as an Atlantic Empire, the role of States goes from being the creating force of slavery to managerial bureaucratic entrepots within a dimension of politics that encompasses difference instead of denying it. The argument is built along 6 chapters (the first being the Introduction). Chapter 2 presents the insufficiency of IR as a discipline, profoundly dependent on the abstract idea of citizenship, to account for slavery. This violent labour exploitation system is disciplinarily incomprehensible either as a project – of keeping the different within the borders – or in the possibility of accounting for the enslaved population itself. This challenge to the disciplinary theoretical framework is the foundation upon which, from the third chapter onwards, the conceptual argument builds through the reading of historiography and archives on slavery. In chapter 3, I address the bibliographies of slavery that deal with enslaved people as labour and the bibliography that characterizes them in their social lives in order to build a more accurate portrait of these people. Chapter 4 focuses on the other cohort of people: the citizens. White men from the US and from Brazil actively maintained slavery and its articulation in their imaginaries of the Atlantic. Chapter 5 addresses the antinomies of Liberalism by considering how it was dependent on slavery at the same time that it operated to make slavery invisible through the lenses with which it reads the 19th Century. In chapter 6, I fully articulate the concept of Empire as a way of interpreting a political dimension that stands above States – without denying them – and whose politics directly impacts on the lives of citizens and non-citizens encompassed within its domains.