After the fall of Göktürk kingdom, Oghuz tribes migrated to the area of Transoxiana, in western Turkestan, in modern Kazakhstan and Kirghizstan. This land became known as the "Oghuz steppe" which is an area between the Caspian and Aral seas. Ibn al-Athir, an Arab historian, stated that the Oghuz Turks had come to Transoxiana in the period of the caliph Al-Mahdi in the years between 775 and 785. In the period of the Abbasid caliph Al-Ma'mun (813–833), the name Oghuz starts to appear in the Islamic historiography. By 780 AD, the eastern parts of the Syr Darya were ruled by the Karluk Turks and the western region (Oghuz steppe) was ruled by the Oghuz Turks.