Geographically, politically, and socially, Transoxiana was divided into four regions: Tokharistan on the upper Oxus, surrounded by the Hissar Mountains to the north and the Hindu Kush to the east and south; Sogdia or Sogdiana, to the east of the middle Oxus and around the Zarafshan river; Khwarezm or Chorasmia, on the lower Oxus and its confluence into the Aral Sea; and the lands north of the Hissar Mountains and along the Jaxartes river (modern Syr Darya), including Zhetysu and the Fergana Valley. As today, the population belonged to two broad linguistic groups: the speakers of Iranian languages, who in the 7th century tended to be urbanized, and the Turkic peoples, who at the time were still mostly nomadic. Indeed, the history of Transoxiana had been dominated by the invasions of nomadic peoples from Central Asia. In the 2nd century BC the Yuezhi destroyed the Greco-Bactrian Kingdom and supplanted it with the Kushan Empire, under which Buddhism entered the area. The Kushans were succeeded by the Hephthalites in the early 5th century, whose dominance lasted until the rise of the First Turkic Khaganate in the mid-6th century. After the great Khaganate became divided in two, the Western Turkic Khaganate retained its position of overlordship over the various principalities of Transoxiana, on occasion even launching raids as far as Balkh.