 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 . 
