Analysing the processes and relationships of political territoriality and collective identity in the American borderlands, this thesis examines the narrative and material dimensions of policies increasingly favouring securitised border 'control'. This 'reterritorialisation' contrasts markedly with concurrent moves to increase economic integration under the North American Free Trade Agreement and with long patterns of transnational socio-cultural interaction, emblematic of larger relational, transnational 'mobilities' fostered by globalisation. Through a historical and transdisciplinary survey, borders are examined as representations and socio-political constructs: a unique, contingent, political cartography connected to a precise, early modern notion of space and identity. Borders are in a continual process of being reproduced through both material means and supportive state-produced 'texts' or narratives. The analysis is part of a larger project in International Relations: the development of the 'identities/borders/orders' heuristic triad, designed to narrow and produce new theoretical and empirical insights by coupling three key concepts and exploring the co-constitutive relationships. Focussing on the identity-border link within the triad, the first case study analyses 'Operation Hold the Line' and related events in the securitisation of the southern borderlands against undocumented migration. The second case study provides an account of major official documentation and public debate framing current developments on the northern border, including a reading of the Illegal Immigration Reform and Immigrant Responsibility Act of 1996. Border policy is understood as an example of reflexive territoriality, suggesting continual, ever speedier revision, monitoring, and reproduction of a state's constructed strategy responding to control defined 'risks', such as migration. These regulations are fed and actualised by new information flows and technologies, as the state's attempt to 'control' its borders by making them political realities of difference with particular material and normative outcomes. Here, the politics of representation involves an image of border 'security' which effects the socio-spatialisation of collective identity, specifically the reinforcement of difference and a secure nationalism narrative. The securitisation also reflects a modern understanding of knowledge as regulation and order.