Orientalist historian, Islamic specialist Professor Claude Kaen, in his work on medieval Turkey, considers it as the forerunner of the Ottoman Empire. Giving a general picture of the great era of the Seljukids, he talks not only about the peculiarities of the Muslim East, but also about the political and religious confrontation of the dynasties inhabiting Asia - the Abbasids, Samanids, Buids, the same Seljukids, etc., as well as various Shiite and Sunni clans... undermining the foundations of hostile regimes. The author pays considerable attention to various social, economic and institutional problems in Turkey of the pre-Mongol period and changes caused by the Mongol invasion, the collapse of the formed empire and the growth of a new type of principalities that arose on the ruins of both the Byzantine and Seljuk states.