This dissertation examines the rise of the Mohajir subnationalist movement in Sindh Province, Pakistan. It focusses on the Mohajir Qaumi Movement (Mohajir National Movement; MQM) - the party that has constructed a version of a Mohajir identity for political purposes. The analysis begins with a critical examination of the Muslim movement in British India, which culminated in the formation of Pakistan. The political history of Pakistan up to 1993 is then examined, with particular reference to the development of subnationalist movements. There then follows a detailed appraisal of debates and theories on identity, ethnicity and nationalism. The second section of the dissertation focusses on the Province of Sindh in southern Pakistan. It introduces the research framework and methodologies, and details the range of interviews conducted and archival and other sources consulted. The section proper examines, firstly, the construction of diverse community identities in Sindh Province, and, secondly, the MQM in terms of its political history, patterns of mobilisation, internal structure and aims and rhetoric. The third section of the dissertation is focussed on the city of Karachi; very much the heartland of the MQM- I first examine how and why the MQM came to be the city's dominant agency in the 1980s, and how it ran a "parallel local state" in urban Sindh. I then consider the relationship between Mohajir subnationalism and violent civil disorder in Karachi and Hyderabad. This analysis in turn highlights certain contradictions in the policies and activities of the MQM. These contradictions are explored at length in a concluding chapter which considers the rise and fall of the MQM in the wider context of stateformation in postcolonial developing countries.