Uyghur Khaganate

The Uyghur Khaganate was the trading empire of the Orkhon Turks, the steppe power that bankrolled the Tang and wrote its laws on city walls. The Nine Clans, led by the Yaglakar house, had served the Göktürks as vassals until 744, when they joined the Basmyl and Karluks to destroy their masters and raised Bayanchur as khagan. Unlike every horde before them, the Uyghurs built a fixed capital, Ordu-Baliq on the Orkhon, with walls, markets and Manichaean temples, and garrisoned it with an administration that taxed the Silk Road in writing. Tang China, bleeding from the An Lushan rebellion, bought Uyghur cavalry with silk by the million bolt, and the khagans lent the emperor armies on condition of tribute, loot and a Chinese princess. Under Bögü Qaghan the court took Manichaeism as its religion, and Sogdian scribes gave the Uyghurs the script that would later serve the Mongols. Drought, the Kyrgyz from the north and a disputed succession ended it: in 840 the Kyrgyz burned Ordu-Baliq, and the Uyghurs scattered to the Tarim oases, where Qocho and Ganzhou kept their script, their Buddhism and their merchant courts alive for five more centuries, until the Mongols took them as tutors.