For a time the Il-Khans tolerated and patronized all religious persuasions—Sunni, Shīʿite, Buddhist, Nestorian Christian, Jewish, and pagan. But in 1295 a Buddhist named Maḥmūd Ghāzān became khan and declared himself Muslim, compelling other Mongol notables to follow suit. His patronage of Islamicate learning fostered such brilliant writers as Rashīd al-Dīn, the physician and scholar who authored one of the most famous Persian universal histories of all time. The Mongols, like other Islamicate dynasties swept into power by a tribal confederation, were able to unify their domains for only a few generations. By the 1330s their rule had begun to be fragmented among myriad local leaders. Meanwhile, on both Mongol flanks, other Turkic Muslim powers were increasing in strength.
To the east the Delhi Sultanate of Turkic slave-soldiers withstood Mongol pressure, benefited from the presence of scholars and administrators fleeing Mongol destruction, and gradually began to extend Muslim control south into India, a feat that was virtually accomplished under Muḥammad ibn Tughluq. Muslim Delhi was a culturally lively place that attracted a variety of unusual persons. Muḥammad ibn Tughluq himself was, like many later Indian Muslim rulers, well-read in philosophy, science, and religion. Not possessing the kind of dynastic legitimacy the pastoralist Mongols had asserted, he tied his legitimacy to his support for the Sharīʿah, and he even sought to have himself invested by the ʿAbbāsid “caliph” whom the Mamlūks had taken to Cairo. His concern with the Sharīʿah coincided with the growing popularity of Sufism, especially as represented by the massive Chishti ṭarīqah. Its most famous leader, Niẓām al-Dīn Awliyāʾ, had been a spiritual adviser to many figures at court before Muḥammad ibn Tughluq came to the throne, as well as to individual Hindus and Muslims alike. In India, Sufism, which inherently undermined communalism, was bringing members of different religious communities together in ways very rare in the more westerly parts of Islamdom.
To the west the similarly constituted Mamlūk state continued to resist Mongol expansion. Its sultans were chosen on a nonhereditary basis from among a group of freed slaves who acted as the leaders of the various slave corps. At the death of one sultan, the various military corps would compete to see whose leader would become the next sultan. The leaders of the various slave corps formed an oligarchy that exercised control over the sultan. Although political instability was the frequent and natural result of such a system, cultural florescence did occur. The sultans actively encouraged trade and building, and Mamlūk Cairo became a place of splendour, filled with numerous architectural monuments. While the Persian language was becoming the language of administration and high culture over much of Islamdom, Arabic alone continued to be cultivated in Mamlūk domains, to the benefit of a diversified intellectual life. Ibn al-Nafīs (died 1288), a physician, wrote about pulmonary circulation 300 years before it was “discovered” in Europe. For Mamlūk administrative personnel, al-Qalqashandī composed an encyclopaedia in which he surveyed not only local practice but also all the information that a cultivated administrator should know. Ibn Khallikān composed one of the most important Islamicate biographical works, a dictionary of eminent men. Sharīʿah-minded studies were elaborated: the ulama worked out a political theory that tried to make sense of the sultanate, and they also explored the possibility of enlarging on the Sharīʿah by reference to falsafah and Sufism.