In 552-555 the Gokturks replaced the Rouran in Mongolia, forming the Turkic Khaganate (552-630). They quickly spread west to the Caspian Sea. Between 581 and 603 the Western Turkic Khaganate in Kazakhstan separated from the Eastern Khaganate in Mongolia. In the early period the Chinese were weak and paid tribute to the Turks. The Chinese grew stronger and overthrew the Eastern Turks in 630.
The sequence of ruling groups was c400-555: Rouran Khaganate; 552-630: Gokturks; 630-682: disunion; 682-744: Second Turkic Khaganate; 744-840: Uyghur Khaganate. The Gokturk rulers were the first dynasty to definitely speak a Turkic language (Orkhon inscriptions). An important part was played by the Sogdian merchants who controlled the silk road trade and advised the Turkic rulers. The Gokturks and Mongols were the only two empires to rule both the eastern and central steppe (modern Mongolia and Kazakhstan).
Before the Khaganate
‘Turk’, meaning something like ‘strong’, was the self-description of the small Ashina clan or tribe. It was later applied to the Gokturk Khaganate and later by Muslim historians to all speakers of Turkic languages. The Chinese equivalent, Tujue,[a] was sometimes applied to many northern peoples and does not always mean 'Turk' in the strict sense. The Chinese report that in 439 a man named Ashina led 500 families west from Gansu to Gaochang near Turfan.  About 460 the Rouran moved them east to the Altai which was an important source of metalwork for Siberia and Mongolia. David Christian says that the first dated mention of ‘Turk’ appears in Chinese annals in 542 when they made annual raids across the Yellow River when it froze over. In 545 the future Bumin Qaghan was negotiating directly with the Western Wei (535-57) without regard to his Rouran overlords. Later the Turks were sent east to suppress a rebellion by the Kao-ch’e, but the Turks absorbed them into their own army. Bumin demanded a royal bride from the Rouran and was denounced as a ‘blacksmith slave’. Bumin took a bride from the Western Wei, defeated the Rouran ruler in Jehol and took the royal title of Khagan (552).
Nominal unity (552-581)
The west was given to Bumin’s younger brother Istämi (552-75) and his son Tardush (575-603). Ishtami expanded the empire to the Caspian and Oxus. The Gokturks somehow gained the Tarim Basin and thus the Silk Road trade and the Sogdian merchants that managed it. Bumin died in the year of his rebellion (552) and was followed by three of his sons. Issik Qaghan (552-53) reigned briefly. Muqan Khagan (553-72) finished off the remaining Rouran, who resisted until 555, pushed the Kitans east and controlled the Yenisei Kirghiz. He was followed by Taspar Qaghan (572-81). The three brothers extracted a large amount of booty and tribute from the Western Wei (535-57) and Northern Zhou (557-581), including 100,000 rolls of silk annually.
East-West split (581-603)
In 581 the Sui dynasty was founded and began to reunify China. The Chinese began pushing back, generally by supporting or bribing one faction against the other. Taspar died the same year the Sui dynasty was founded. The three claimants were the sons of the three previous rulers. Taspar chose Muqan’s son Apa Qaghan, but the elders rejected this and chose Taspar’s son Anlo (581). Anlo soon yielded to Issik's son Ishbara Qaghan (581-87). Anlo became insignificant and Apa and Ishbara fought it out. In 584 Ishbara attacked Apa and drove him west to Bumin's brother Tardush, who ruled what was becoming the Western Khaganate. Apa and Tardush then drove Ishbara east. He submitted to the Chinese and with Chinese support drove Apa west into Tardush’s territory. In 587 both Apa and Ishbara died. See Gokturk civil war. Ishbara was followed in the east by his brother Bagha Qaghan (587-88) who was followed by Ishbara’s son Tulan Qaghan (588-99). In 587 Tulan stopped paying tribute to the Sui and two years later was assassinated. Tardush moved from the west and briefly reunified the Turkic empire (599-603). The Chinese supported his rivals, he attacked China, the Chinese poisoned the wells and he was forced to retreat.
From 603 the east and west were definitely split. The east went to Yami Qaghan (603-09) as a sort of Chinese vassal. He admired Chinese culture and had the Chinese build him a civilized house in the Ordos country.
As the Sui Dynasty's power waned, separatist Chinese leaders agreed to become vassals of Shibi Qaghan (609-19) and adopted Turkic-style titles, as well as the Khaganate's wolf's-head banners. In 615, the Chinese lured his Sogdian advisor into a trap and killed him. He stopped paying tribute and briefly besieged Emperor Yang of Sui in Shanxi.
In 615 Emperor Yang assigned Li Yuan, who would later become the first emperor of the Tang Dynasty, the impossible task of protecting the Sui dynasty's northern border. In 617, when tens of thousands of Turks reached Taiyuan, they found the gates open and the city suspiciously quiet. Fearing an ambush, the Turk's retreated. Li Yuan's deception had been successful and he quickly pressed his advantage offering the Turks "prisoners of war, women, jade and silks" in return for their friendship. The Turks declined, demanding instead that Li Yuan become a "Son of Heaven" and accept a Turkic title and banner.
Shibi's younger brother Chuluo (619-20) ruled for only 18 months. The next brother, Illig Qaghan (620-30), was the last independent ruler. He led yearly raids against the new Tang dynasty (618-907). In 626 he reached the gates of Chang’an. Emperor Taizong of Tang, who had just overthrown his father, chose to pay an enormous ransom. Taizong waited and enlarged his cavalry. In 627-29 unusual cold led to mass livestock deaths and famine. Instead of lowering taxes, Illig raised them. The Xueyantuo, Uyghurs, Bayegu and some of Illig’s people rebelled and in 629 were joined by the Kitan and Taizong. Six Chinese armies attacked in a 1200 kilometer front and Illig was captured (630). See Tang campaign against the Eastern Turks.
After the First Khaganate (630-683)
After the fall of the Khaganate Zhenzhu Khan (629-45) of the Xueyantuo ruled much of the north. Taizong made the Ashina live inside the Ordos Loop. In 639, after an Ashina assassination attempt, Taizong made them live between the Yellow River and Gobi under Qilibi Khan (639-43) as a buffer state between China and the Xueyantuo. In 642 the Xueyantuo drove them south of the river. (See Tang campaign against the Eastern Turks#Aftermath in Mongolia.) Zhenzhu’s son Duomi Khan (645-46) planned to attack China. Taizong allied with the Uyghurs and broke up the Xueyantuo clan. The Ashina Chebi Khan (646-50) tried to revive the Khaganate but was captured by the Chinese and Uyghurs. Two more attempts by Ashina Nishufu (679-80) and Ashina Funian (680-681) failed. Turkic power was restored by the Second Turkic Khaganate (682-744), followed by the Uyghur Khaganate (744-840).