 The rise of al-Mu 'tasim to the caliphate was a watershed moment in the history of the Abbasid state, heralding a radical change in the nature of its administration. Unlike his brother, who tried to use the Arabs and Turks to balance out the Iranian troops, al-Mu'tasim relied almost exclusively on his Turks, and established "a new regime that was militaristic and centred on the Turkish corps" (Tayeb El-Hibri). This was a decision with long-lasting repercussions in Islamic history. Not only did the military acquire a predominant position, but it also increasingly became the preserve of minority groups from the peoples living on the margins of the Islamic world. Thus it formed an exclusive ruling caste, separated from the Arab-Iranian mainstream of society by ethnic origin, language, and sometimes even religion. This dichotomy would become a "distinctive feature" (Hugh N. Kennedy) of many Islamic polities, and would culminate in the Mamluk dynasties that ruled Egypt and Syria in the late Middle Ages.
