Of the last, occurring mainly in the north, the chief are the longitudinal valley stretching from near the Herat frontier through Meshed, Kuchan and Shirvan to Bujnurd, the Derrehgez district, which lies on the northern skirt of the outer range projecting into the Akhal Tekkeh domain, now Russian territory, and the districts of Nishapur and Sabzevar which lie south of the Binalud and Jagatai ranges.
The Persian Empire under Hulagu and his descendants extended from the dominions of Jagatai on the north to that of the Egyptian dynasts on the south, and from the Byzantine Empire on the west to the confines of China.
Great-grandson of Karachar Nevian (minister of Jagatai, son of Jenghiz Khan, and commander-in-chief of his forces), and distinguished among his fellow-clansmen as the first convert to Islamism, Teragai might have assumed the high military rank which fell to him by right of inheritance; but like his father Burkul he preferred a life of retirement and study.
The Uzbegs, who played a predominant political part in Turkestan before the Russian conquest, are of Turko-Tatar origin and speak a pure Jagatai (Turkish) dialect; but they are mixed to a great extent with Persians, Kirghiz and Mongols.
His invasion gave a decided check to the progress of the Mahommedan creed, but on his death, and during the rule of the Jagatai Khans, who became converts to that faith, it began to reassert its ascendancy.