Thus in the year A.H. 350 (961), on the death of `Abd el-Melik I., Mansūr I., his brother and successor, met with serious opposition from a certain Turk named Alptagin, governor of Nīshāpūr, who refused to recognise his claims. Resort was had to arms, and, after a battle at Balkh, the results of which are variously stated, Alptagin withdrew to Ghazna, where he established himself so strongly that he was able to repulse the army sent by Mansūr to attack him. On the death of Alptagin in A.H. 366 (976) the leadership of those men who had accompanied him to Ghazna passed to another Turk named Sabuktagin. The choice was fortunate, for Sabuktagin proved himself to be a general of great talent; and by means of little frontier engagements he succeeded in rapidly extending his territories, and ultimately in founding a powerful dynasty which, under his successor, was to bring Northern India, Persia, and the East under its sway. Although Sabuktagin was the nominal vassal of the Sāmānides,[243] he was in reality an independent ruler. This was, moreover, the case in a lesser or greater degree with many of the governors in Khorāsān and the neighbouring dependencies. CHAPTER XVI THE KARA-KHĀNIDES, OR UÏGHŪRS While the Sāmānides were thus harassed by the powerful Daylamites in the west, by the growing power of Sabuktagin in the south, and the fear of insubordination in their own states, a force still more formidable had arisen on their northern frontier, where a Turkish state had been founded which extended from Kāshghar to the Sea of Aral. The relations of this state with its southern neighbours were at first of a peaceful and even friendly character; but when the nomads perceived that Iranian authority was on the wane they began to cast longing eyes across the Jaxartes. They probably belonged to the tribe of _Uïghūr_, which had been the first to separate from the main body of the Turkish race and settle down in a home on the slopes of the Tien-shan.[244] According to the Mohammedan historian Juvaynī,[245] the Uïghūrs originally came from the valley of the Orkon River. The first king whose name has come down to us was Būkū Khān, whom tradition has identified with the great Afrāsiyāb.[246]