The prevailing image of the Indian Ocean world of trade before the arrival of western Europeans and Ottomans in the region in the sixteenth century is one of a generally peaceful, conflict-free realm dominated by cosmopolitan traders who moved easily across boundaries of geography, ethnicity, language, and religion. This paper modifies this picture by examining the evidence for conflict and competition between pre-modern maritime polities in the western end of the Indian Ocean. In the fifth/eleventh and sixth/twelfth centuries maritime polities on the islands of Kish in the Persian Gulf and Dahlak in the Red Sea antagonized Aden's supremacy as the region's most frequented entrepot. In the subsequent three centuries, the Ayyubids and Rasulids of Yemen also strove to control maritime routes and networks. [ABSTRACT FROM AUTHOR]