 Complete the following phrase:  Thus, in the Islamic period, dark-skinned Africans in the Arabian Peninsula and elsewhere in Caliphate tended to be slaves. For example, al-Ṭabarī estimated that in Southern Basra alone there were around 15,000 around the 870s. This situation encouraged Arabs to view themselves as superior to Black people, not least as a mechanism for Arabs to justify the enslavement of others. For example, Ibn Buṭlān composed a noted, stereotyping description of the qualities of slaves of different races, which is relatively positive about Nubians, but otherwise particularly negative about the characteristics of Black people. The Egyptian historian al-Abshibi d. 1446 wrote that it is said that when the black slave is sated, he fornicates, when he is hungry, he steals. Allegedly, such was his distrust of Black people, Abu Muslim al-Khurasani massacred four thousand of his own Black soldiers after completing the 