The ruling Mongol elites of these Khanates eventually assimilated into the Turkic populations that they conquered and ruled over, thus becoming known as Turco-Mongols. These elites gradually adopted Islam (from previous religions like Tengrism) as well as Turkic languages, while retaining Mongol political and legal institutions.
The Mongols during the period of the early Mongol conquests and the conquests of Genghis Khan largely followed Tengrism. However, the successor states of the Mongol Empire, the Ilkhanate, Golden Horde and Chagatai Khanate ruled over large Muslim populations with the Ilkhanate and Chagatai Khanate ruling over Muslim majority populations in Iran and Central Asia respectively.
In the Golden Horde, Uzbeg (Öz-Beg) assumed the throne in 1313 and adopted Islam as the state religion. He proscribed Buddhism and Shamanism among the Mongols in Russia, thus reversing the spread of the Yuan culture. By 1315, Uzbeg had successfully Islamicized the Horde, killing Jochid princes and Buddhist lamas who opposed his religious policy and succession of the throne. Uzbeg Khan continued the alliance with the Mamluks begun by Berke and his predecessors. He kept a friendly relationship with the Mamluk Sultan and his shadow Caliph in Cairo. After a long delay and much discussion, he married a princess of the blood to Al-Nasir Muhammad, Sultan of Egypt. Under Uzbeg and his successor Janibeg (1342-1357), Islam, which among some of the Turks in Eurasia had deep roots going back into pre-Mongol times, gained general acceptance, though its adherents remained tolerant of other beliefs. In order to successfully expand Islam, the Mongols built a mosque and other "elaborate places" requiring baths -- an important element of Muslim culture. Sarai attracted merchants from other countries. The slave trade flourished due to strengthening ties with the Mamluk Sultanate. Growth of wealth and increasing demand for products typically produce population growth, and so it was with Sarai. Housing in the region increased, which transformed the capital into the center of a large Muslim Sultanate.
Before the time of Genghis Khan, Turkic peoples and Mongols exchanged words between each other, with Turkic languages being more active than Mongolian. A much earlier Turco-Mongol tradition existed in, as evidenced by the extensive lexical borrowings from Proto-Turkic in the Proto-Mongolic language from around at least the first millennium BCE. Turkic and Mongolic languages share extensive borrowed similarities in their personal pronouns, among other lexical similarities, which seem to date to before this era and already existed before the breakup of the Turkic people around 500 BCE. A still more ancient period of prolonged language contact between Turkic and Mongol languages is indicated by further and more fundamental phonotactic, grammatical, and typological similarities (e.g. synchronic vowel harmony, lack of grammatical gender, extensive agglutination, highly similar phonotactic rules and phonology). In the past, such similarities were attributed to a genetic relationship and led to the widespread acceptance of an Altaic language family. More recently, due to the lack of a definitive demonstration of genetic relationship, these similarities have been divided into at these three known periods of language contact. The similarities have led to the proposal of a Northeast Asian sprachbund instead, which also includes the Tungusic, Korean, and Japonic language families, although Turkic and Mongolic display the most extensive similarities. According to recent aggregation and research, there are doublets, which are considered to be the same in terms of their roots, found in the vocabulary in Mongolian language and Turkic loanwords. Also, inside the Mongolian vocabulary that are derived from other languages, Turkic is the most common.
Following the Mongol conquests, the ruling Mongol elites of the Mongol successor states began a process of assimilation with the non-Mongol populations that they ruled over. The population of the Golden Horde was largely a mixture of Turks and Mongols who adopted Islam later, as well as smaller numbers of Finno-Ugrians, Sarmato-Scythians, Slavs, and people from the Caucasus, among others (whether Muslim or not). Most of the Horde's population was Turkic: Kipchaks, Cumans, Volga Bulgars, Khwarezmians, and others. The Horde was gradually Turkified and lost its Mongol identity, while the descendants of Batu's original Mongol warriors constituted the upper class. They were commonly named the Tatars by the Russians and Europeans. Russians preserved this common name for this group down to the 20th century. Whereas most members of this group identified themselves by their ethnic or tribal names, most also considered themselves to be Muslims. Most of the population, both agricultural and nomadic, adopted the Kypchak language, which developed into the regional languages of Kypchak groups after the Horde disintegrated.
In the Chagatai Khanate, the Turkic language that was adopted by the Mongol elites became known as the Chagatai language, a descendant of Karluk Turkic. The Chagatai language was the native language of the Timurid dynasty, a Turco-Mongol dynasty who would gain power in Central Asia after the decline of the Chagatai Khans.