section_path: Military and foreign policy/Western and Northern regions
section_name: Western and Northern regions
paragraph_text: Western and Northern regions
  
  The Sui and Tang carried out successful military campaigns against the steppe nomads. Chinese foreign policy to the north and west now had to deal with Turkic nomads, who were becoming the most dominant ethnic group in Central Asia. To handle and avoid any threats posed by the Turks, the Sui government repaired fortifications and received their trade and tribute missions. They sent four royal princesses to form marriage alliances with Turkic clan leaders, in 597, 599, 614, and 617. The Sui stirred trouble and conflict amongst ethnic groups against the Turks. As early as the Sui dynasty, the Turks had become a major militarized force employed by the Chinese. When the Khitans began raiding northeast China in 605, a Chinese general led 20,000 Turks against them, distributing Khitan livestock and women to the Turks as a reward. On two occasions between 635 and 636, Tang royal princesses were married to Turk mercenaries or generals in Chinese service. Throughout the Tang dynasty until the end of 755, there were approximately ten Turkic generals serving under the Tang. While most of the Tang army was made of fubing Chinese conscripts, the majority of the troops led by Turkic generals were of non-Chinese origin, campaigning largely in the western frontier where the presence of fubing troops was low. Some "Turkic" troops were tribalized Han Chinese, a desinicized people.
  
  Civil war in China was almost totally diminished by 626, along with the defeat in 628 of the Ordos Chinese warlord Liang Shidu; after these internal conflicts, the Tang began an offensive against the Turks. In the year 630, Tang armies captured areas of the Ordos Desert, modern-day Inner Mongolia province, and southern Mongolia from the Turks. After this military victory, On June 11, 631, Emperor Taizong also sent envoys to the Xueyantuo bearing gold and silk in order to persuade the release of enslaved Chinese prisoners who were captured during the transition from Sui to Tang from the northern frontier; this embassy succeeded in freeing 80,000 Chinese men and women who were then returned to China.
  
  While the Turks were settled in the Ordos region (former territory of the Xiongnu), the Tang government took on the military policy of dominating the central steppe. Like the earlier Han dynasty, the Tang dynasty (along with Turkic allies) conquered and subdued Central Asia during the 640s and 650s. During Emperor Taizong's reign alone, large campaigns were launched against not only the Göktürks, but also separate campaigns against the Tuyuhun, the oasis city-states, and the Xueyantuo. Under Emperor Gaozong, a campaign led by the general Su Dingfang was launched against the Western Turks ruled by Ashina Helu.
  
  The Tang Empire competed with the Tibetan Empire for control of areas in Inner and Central Asia, which was at times settled with marriage alliances such as the marrying of Princess Wencheng (d. 680) to Songtsän Gampo (d. 649). A Tibetan tradition mentions that Chinese troops captured Lhasa after Songtsän Gampo's death, but no such invasion is mentioned in either Chinese annals or the Tibetan manuscripts of Dunhuang.
  
  There was a long string of conflicts with Tibet over territories in the Tarim Basin between 670 and 692, and in 763 the Tibetans even captured Chang'an for fifteen days during the An Shi Rebellion. In fact, it was during this rebellion that the Tang withdrew its western garrisons stationed in what is now Gansu and Qinghai, which the Tibetans then occupied along with the territory of what is now Xinjiang. Hostilities between the Tang and Tibet continued until they signed a formal peace treaty in 821. The terms of this treaty, including the fixed borders between the two countries, are recorded in a bilingual inscription on a stone pillar outside the Jokhang temple in Lhasa.
  
  During the Islamic conquest of Persia (633–656), the son of the last ruler of the Sassanid Empire, Prince Peroz and his court moved to Tang China. According to the Old Book of Tang, Peroz was made the head of a Governorate of Persia in what is now Zaranj, Afghanistan. During this conquest of Persia, the Rashidun Caliph Uthman Ibn Affan (r. 644–656) sent an embassy to the Tang court at Chang'an. Arab sources claim Umayyad commander Qutayba ibn Muslim briefly took Kashgar from China and withdrew after an agreement, but modern historians entirely dismiss this claim. The Arab Umayyad Caliphate in 715 deposed Ikhshid, the king the Fergana Valley, and installed a new king Alutar on the throne. The deposed king fled to Kucha (seat of Anxi Protectorate), and sought Chinese intervention. The Chinese sent 10,000 troops under Zhang Xiaosong to Ferghana. He defeated Alutar and the Arab occupation force at Namangan and reinstalled Ikhshid on the throne. The Tang dynasty Chinese defeated the Arab Umayyad invaders at the Battle of Aksu (717). The Arab Umayyad commander Al-Yashkuri and his army fled to Tashkent after they were defeated. The Turgesh then crushed the Arab Umayyads and drove them out. By the 740s, the Arabs under the Abbasid Caliphate in Khorasan had reestablished a presence in the Ferghana basin and in Sogdiana. At the Battle of Talas in 751, Karluk mercenaries under the Chinese defected, helping the Arab armies of the Caliphate to defeat the Tang force under commander Gao Xianzhi. Although the battle itself was not of the greatest significance militarily, this was a pivotal moment in history, as it marks the spread of Chinese papermaking into regions west of China as captured Chinese soldiers shared the technique of papermaking to the Arabs. These techniques ultimately reached Europe by the 12th century through Arab-controlled Spain. Although they had fought at Talas, on June 11, 758, an Abbasid embassy arrived at Chang'an simultaneously with the Uighur Turks bearing gifts for the Tang Emperor. In 788–789 the Chinese concluded a military alliance with the Uighur Turks who twice defeated the Tibetans, in 789 near the town of Gaochang in Dzungaria, and in 791 near Ningxia on the Yellow River.
  
  Joseph Needham writes that a tributary embassy came to the court of Emperor Taizong in 643 from the Patriarch of Antioch. However, Friedrich Hirth and other sinologists such as S.A.M. Adshead have identified Fu lin (拂菻) in the Old and New Book of Tang as the Byzantine Empire, which those histories directly associated with Daqin (i.e. the Roman Empire). The embassy sent in 643 by Boduoli (波多力) was identified as Byzantine ruler Constans II Pogonatos (Kōnstantinos Pogonatos, or "Constantine the Bearded") and further embassies were recorded as being sent into the 8th century. S.A.M. Adshead offers a different transliteration stemming from " patriarch " or " patrician ", possibly a reference to one of the acting regents for the young Byzantine monarch. The Old and New Book of Tang also provide a description of the Byzantine capital Constantinople, including how it was besieged by the Da shi (大食, i.e. Umayyad Caliphate) forces of Muawiyah I, who forced them to pay tribute to the Arabs. The 7th-century Byzantine historian Theophylact Simocatta wrote about the reunification of northern and southern China by the Sui dynasty (dating this to the time of Emperor Maurice); the capital city Khubdan (from Old Turkic Khumdan, i.e. Chang'an); the basic geography of China including its previous political division around the Yangtze River; the name of China's ruler Taisson meaning " Son of God ", but possibly derived from the name of the contemporaneous ruler Emperor Taizong.