In the 6th century, 400 years after the collapse of northern Xiongnu power in Inner Asia, leadership of the Turkic peoples was taken over by the Göktürks. Formerly in the Xiongnu nomadic confederation, the Göktürks inherited their traditions and administrative experience. From 552 to 745, Göktürk leadership united the nomadic Turkic tribes into the Göktürk Empire. The name derives from "gok", "blue" or "celestial". Unlike its Xiongnu predecessor, the Göktürk Khanate had its temporary "khans" from the Ashina clan that were "subordinate" to a sovereign authority controlled by a council of tribal chiefs. The Khanate retained elements of its original shamanistic religion, Tengriism, although it received missionaries of Buddhist monks and practiced a syncretic religion. The Göktürks were the first Turkic people to write Old Turkic in a runic script, the Orkhon script. The Khanate was also the first state known as "Turk". Towards the end of the century, the Göktürks Khanate was split in two; i.e., Eastern Turkic Khaganate and Western Turkic Khaganate. The Tang Empire conquered the Eastern Turkic Khaganate in 630 and the Western Turkic Khaganate in 657 in a series of military campaigns. However in 681 the khanate was revived. The Göktürks eventually collapsed due to a series of dynastic conflicts, but the name "Turk" was later taken by many states and peoples.