This thesis examines the political career of Abdallah bin al-Husayn from 1908 until the creation of the Emirate of Transjordan in 1921. The central aim here is to explain how Abdallah was transformed from a Hijazi notable to a major force in the post-war politics of the Fertile Crescent and the founder of the Emirate of Transjordan. Abdallah's political career until 1921 is studied in the context of his family's evolving political ambitions and Anglo-Hashimite and Hashimite-Arab nationalist relations. Abdallah's early political career illuminates the changing character of Arab political leadership in the Arab East between 1914 and 1921. This thesis examines the shaping of Abdallah's political ambitions, the strategies Abdallah, his family and partisans adopted to realize those ambitions and the obstacles Abdallah faced in trying to establish his authority and the legitimacy of his rule, first, in Iraq and, later, in Transjordan. Examining these issues in the context of Anglo-Hashimite and Hashimite-Arab nationalist relations makes it possible to assess Abdallah's contribution to the emergence of new forms of Arab political leadership in the post-war Fertile Crescent, particularly in Transjordan and Iraq, and to the development of Arab nationalism. Chapters one to four analyze the shaping of Abdallah's political ambitions in the wider context of evolving Hashimite ambitions during World Var I. Chapters five to eight treat two closely related subjects: Abdallah's failure to realize his ambition to rule post-war Iraq and his role in the creation of the Emirate of Transjordan.