Complex sentence: Early in the thirteenth century, the territory of Anatolia was reorganized, as Turkmen tribes known as the Oghuz Turks, arriving with the Seljuks in the late eleventh century had organized themselves into independent sovereignties, the Beyliks.
Split into simpler sentences: Early in the thirteenth century, the territory of Anatolia was reorganized. By this time, Turkmen tribes known as the Oghuz Turks, who had arrived with the Seljuqs in the late eleventh century, had organized themselves into independent sovereignties, the Beyliks.