The military of the Tang dynasty was staffed with a large population of Turkic soldiers, referred to as Tujue (突厥) in Chinese sources. Tang elites in northern China were familiar with Turkic culture, a factor that contributed to the Tang acceptance of Turkic recruits. The Tang emperor Taizong adopted the title of "Heavenly Kaghan" and promoted a cosmopolitan empire. Turkic soldiers that served under the Tang dynasty originated from the Eastern Turkic Khaganate. It began with Tang dynasty Emperor Taizong who sent his general Li Jing, eventually ended in defeating the Eastern Turks and capturing their leader Jiali Khan.
Taizong regularly recruited and promoted military officers of Turkic ancestry, whose steppe experience contributed to the western and northern expansion of the Tang empire. The Turkic general Ashina She'er participated in the Tang capture of the Karakhoja, Karasahr, and Kucha kingdoms in Xinjiang. The half-Turkic general An Lushan started a revolt that led to the decline of the Tang dynasty.
The Orkhon inscriptions by the Gokturks were critical of the Turks that had served the Tang dynasty, and condemned them for helping the Chinese emperor expand his burgeoning empire. The Turkic soldiers stationed by the Chinese in the Tang garrisons of Central Asia settled in the region, spreading Turkic languages in the area.
Background
The empire of the Tang dynasty was cosmopolitan and diverse. The Tang dynasty elites of northern China had an interest in Turkic culture and intermingled with the people of the steppes. The setting of one Tang poem describes a yurt, and the performance of a Turkic actress was hosted in the emperor's palace Following the Tang dynasty's defeat of the Eastern Turkic Khaganate, the government authorized the settlement of Turks along the borders of the Tang empire. Turkic officers of the former khaganate were recruited as generals in the Tang military, and their experience with steppe warfare contributed to the Tang's military successes as it expanded westward.
Emperor Taizong and multiculturalism
Emperor Taizong, also known by his personal name Li Shimin, was familiar with the culture of the steppe nomads and employed military strategies using steppe tactics as a prince. Taizong was a skilled horseman, and during a celebration of his victory and ascension to the throne, sacrificed a horse in a ritual derived from a Turkic religious practice. He was able to outmaneuver the heavy cavalry of the Sui dynasty with his light cavalry, a characteristic of steppe warfare. Taizong shared personal relationships with Turkic allies as a prince, reinforced through oaths sworn as blood brothers. His later successes as an emperor against the armies of Central Asia through diplomacy and divide and rule are the result of his early experiences with Turkic culture.
Taizong's adoption of the Heavenly Kaghan title was used to legitimize his role as a steppe khan not solely as a Chinese emperor with the title of Son of Heaven. He valued the kaghan title and was sincere about his role as a leader of Central Asia. He sought to solidify his claim as a kaghan by organizing a gathering of Turkic leaders in the Lingzhou fortress during the last years of his reign to reconfirm his title.
While mostly symbolic, the title of Heavenly Kaghan shows Taizong's open attitudes towards the existence of a multicultural and ethnically diverse Tang empire. Taizong was proud of his policies promoting ethnic equality, and was reported to have said that, "The emperors since ancient times have all appreciated the Chinese and depreciated the barbarians. Only I view them as equal. That is why they look upon me as their parent."
He had a paternalistic attitude towards his subjects and believed that it was his duty to treat the Chinese and foreign ethnic groups as equals under one ruler. Taizong's views grew into state policy as his government recruited Turkic and other non-Han Chinese soldiers into the Tang military. Turkic soldiers were later promoted to higher ranks as commanders and generals. The surname of Li, belonging to the royal family of Li Shimin, was awarded to Han and non-Han officers for their service.
Tang relationship with the Turks may have further deepened had the crown prince Li Chengqian, a Turkophile, been enthroned as Taizong's successor. Li Chengqian enthusiastically embraced Turkic customs, and Chinese historian Sima Guang recorded that he: