Emperor Taizong ' s campaign against Xueyantuo Emperor Taizong of Tang ( r . 626 - 649 ) , the second emperor of Chinese dynasty Tang Dynasty , early in his reign , had allied with Xueyantuo , a vassal of the powerful Eastern Tujue ( Göktürk ) Khanate , against Eastern Tujue , who Tang defeated in 630 . Upon Eastern Tujue ' s defeat , Xueyantuo ' s Zhenzhu Khan Yi ' nan took over Eastern Tujue ' s former territory , and while he was formally submissive to Tang , he was expanding his own strength . When Emperor Taizong tried to restore Eastern Tujue in 639 under the Qilibi Khan Ashina Simo ( also known as Li Simo ) to counteract the rise of Xueyantuo power , Xueyantuo engaged in multiple battles with the newly restored Eastern Tujue , in order to prevent this return . The major Tang general Li Shiji temporarily came to protect Eastern Tujue against Xueyantuo and defeated the Xueyantuo forces in 641 . But in 644 , with Emperor Taizong occupied with a campaign against Goguryeo , Xueyantuo forces launched a new campaign , defeated Eastern Tujue , forcing Ashina Simo to flee back to Tang . Subsequently , Goguryeo sought aid from Xueyantuo , but Yi ' nan avoided further conflict , wanting to avoid direct battle with Tang . After Yi ' nan ' s death in 645 , however , his son , the Duomi Khan Bazhuo began heavily battling Tang forces . In 646 , Tang forces counterattacked , and after they defeated Bazhuo , Xueyantuo ' s vassal Huige rose and killed him . His cousin , the Yitewushi Khan Duomozhi , surrendered to Tang forces , ending Xueyantuo . Cooperation between Tang and Xueyantuo under Yi ' nan . Xueyantuo had been long been a member tribe of the Chile confederation , which had in turn been submissive to Tujue , both before and after Tujue ' s division into Western Tujue and Eastern Tujue , and in the 600s , the Chile had rebelled against Western Tujue ' s Heshana Khan Ashina Daman , declaring independence under the leadership of Qibi ( 契苾 ) chieftain Geleng ( 歌楞 ) ( with the title Yiwuzhenmohe Khan ( 易勿真莫賀可汗 ) ) and the Xueyantuo chieftain Yishibo ( with the title Yiedie Khan ) , but later resubmitted to Western Tujue ' s Shekui Khan . At some point , the Chile became submissive to Eastern Tujue instead , and as of the reign of the Jiali Khan Ashina Duobi , the Xueyantuo were ruled by Yishibo ' s grandson Yi ' nan . However , Ashina Duobi was said to be a poor ruler , and by 627 , several members of the Chile — Xueyantuo , Huige , and Bayegu ( 拔野谷 ) had rebelled . Ashina Duobi tried to send his nephew Ashina Yugu against Huige , but Ashina Yagu was defeated by the Huige chieftain Pusa ( 菩薩 ) , while Xueyantuo defeated four other Eastern Tujue generals , and Ashina Duobi was not able to resubjugate the Chile rebels . Still , in 628 , when these Chile tribes offered the title of khan to Yi ' nan , Yi ' nan did not initially dare to accept it . However , Emperor Taizong of Tang , hearing this and wanting to establish an alliance with Xueyantuo against Eastern Tujue , sent his general Qiao Shiwang ( 喬師望 ) to Xueyantuo to create Yi ' nan the Zhenzhupieqie Khan ( or Zhenzhu Khan in short ) , and subsequently , a large number of Chile and Tujue tribes came under Yi ' nan ' s rule . Subsequently , Tang and Xueyantuo often exchanged emissaries , and Xueyantuo grew stronger at Eastern Tujue ' s expense . In 629 , Emperor Taizong commissioned the general Li Jing to lead a major expedition against Eastern Tujue , and in 630 , Li Jing captured Ashina Duobi and effectively destroyed Eastern Tujue . Much of the Eastern Tujue people surrendered to Xueyantuo , and some surrendered to Tang . After this event , Xueyantuo was the predominant power north of China , but remained formally submissive to Tang . In 638 , Emperor Taizong , with Yi ' nan ' s concurrence , further created Yi ' nan ' s sons Bazhuo and Jialibi ( 頡利苾 ) as subordinate khans under Yi ' nan — ostensibly to honor them , but hoping to create dissension between them . In 639 , when Emperor Taizong commissioned the general Hou Junji to launch a campaign against Gaochang , Yi ' nan offered to attack Gaochang at the same time , although Hou ' s quick conquest of Gaochang appeared to involve no actual Xueyantuo aid . Conflict of 641 . Also in 639 , however , a Tang action would begin to lead to a deterioration of the relationship between Tang and Xueyantuo . After Ashina Duobi ' s capture , Emperor Taizong had settled the Eastern Tujue people who surrendered to Tang within Tang borders , without creating a new khan to govern them . However , after he ( Emperor Taizong ) was nearly assassinated by Ashina Duobi ' s nephew Ashina Jiesheshuai ( 阿史那結社率 ) in 639 , Emperor Taizong changed his mind and created an Eastern Tujue prince loyal to Tang , Ashina Simo as Qilibi Khan ( not to be confused with Yi ' nan ' s son Qilibi ) , to serve as the new khan of Eastern Tujue , intending to settle his state south of the Gobi Desert to serve as a buffer between Tang and Xueyantuo . Yi ' nan was distressed by the development , but initially indicated that he accepted it . As of 641 , Ashina Simo had finally marched north of the Great Wall and settled in at Dingxiang ( 定襄 , in modern Hohhot , Inner Mongolia ) . Meanwhile , Yi ' nan had heard that Emperor Taizong was about to offer sacrifices to heaven and earth at Mount Tai and , believing that the Tang troops would all be with Emperor Taizong , had his son Dadu ( 大度 ) launch a major attack on Eastern Tujue , intending to destroy Ashina Simo before Tang could render aid . Ashina Simo withdrew within the Great Wall and took up position at Shuo Prefecture ( 朔州 , roughly modern Shuozhou , Shanxi ) and sought emergency aid from Tang . Emperor Taizong sent the general Li Shiji , assisted by the generals Zhang Jian ( 張儉 ) , Li Daliang ( 李大亮 ) , Zhang Shigui ( 張士貴 ) , and Li Xiyu ( 李襲譽 ) , to attack Xueyantuo . Li Shiji engaged Dadu first and defeated him , forcing him to flee . Meanwhile , Yi ' nan had sent an emissary to Emperor Taizong to offer peace with Eastern Tujue , and Li Shiji prevailed over Dadu , Emperor Taizong sent the emissary back with a rebuke for Yi ' nan but did not further take actions against Xueyantuo , and thereafter , the relationship between Tang and Xueyantuo officially remained that of lord and vassal , but appeared to be no longer as strong as it formerly was . Later years of Yi ' nan reign . In 642 , Yi ' nan began an attempt to cement his relationship with Tang by sending his uncle Nishou ( 泥熟 ) to Tang to request marriage with one of Emperor Taizong ' s daughters , offering tributes of horses , mink coats , and a mirror made of amber . Meanwhile , with the Tang general Qibi Heli ( 契苾何力 ) - - the chief of the Qibi tribe , a constituent tribe of the Chile as well — being detained in Xueyantuo after he , on a visit back to his tribe , was seized by his own subordinates and taken to Xueyantuo ( as his subordinates wanted to submit to Xueyantuo rather than Tang ) , Emperor Taizong , concerned about Qibi Heli ' s safety ( as Qibi Heli had refused to submit to Xueyantuo , cutting off an ear to show his resolve , causing Yi ' nan to nearly execute him ) , agreed to the marriage proposal , sending the official Cui Dunli to negotiate with Yi ' nan the terms , under which Emperor Taizong ' s daughter Princess Xinxing would marry Yi ' nan , in exchange for Qibi Heli ' s release . In 643 , Yi ' nan again sent his nephew Tuli ( 突利 ) to offer tributes of 50 , 000 horses , 10 , 000 cattle or camels , and 100 , 000 goats , to serve as bride price . Emperor Taizong welcomed Tuli in a grand ceremony , and Tuli held a great banquet in Emperor Taizong ' s honor , which Emperor Taizong and his officials personally attended . However , at Qibi ' s urging , Emperor Taizong was considering renouncing the marriage — initially ordering Yi ' nan to personally meet him and Princess Xinxing at Ling Prefecture ( 靈州 , roughly modern Yinchuan , Ningxia ) to marry her , believing that Yi ' nan would refuse and that he would then have a good excuse to break off the marriage . When Yi ' nan agreed to go to Ling Prefecture , Emperor Taizong found another excuse — that the bride price offered had not been all collected ( as , in order to gather the livestock making up the bride price , Yi ' nan had to collect them from subordinate tribes , and it was taking longer than thought , and the livestock were also dying from having to go through the Gobi ) - - to cancel the marriage treaty , despite strong opposition from his official Chu Suiliang , who pointed out that , effectively , he was devaluing his own words . Emperor Taizong rationalized his decision by arguing that if Yi ' nan had married a Tang princess , he would have greater legitimacy over the Chile tribes and would be more difficult to control . Meanwhile , Yi ' nan was continuing to attack Eastern Tujue periodically . When Emperor Taizong sent emissaries to try to stop him from doing so , Yi ' nan responded : By the end of 644 , the Eastern Tujue people , who were not whole - heartedly supportive of Ashina Simo in the first place , collapsed in light of Xueyantuo threat , fleeing back to Tang territory , and were again settled there . Ashina Simo also went back to Tang and again became a Tang general , ending Tang ' s attempt to recreate Eastern Tujue as a vassal state . This caused Emperor Taizong to be displeased , and when Yi ' nan subsequently sent an emissary to offer tribute to Emperor Taizong , who was at that time deeply into preparation to attack Goguryeo , Emperor Taizong responded , " Go back and tell your khan : My son and I are now about to attack Goguryeo . If he thinks that he can take advantage of this , he is welcome to come ! " Yi ' nan , fearful of Emperor Taizong ' s anger , sent another emissary to apologize and offering to assist in the operation against Goguryeo , an offer that Emperor Taizong declined . In 645 , after Emperor Taizong had defeated the main Goguryeo forces at Mount Zhubi ( 駐驆山 ) , near the fortress of Anshi ( 安市 , in modern Anshan , Liaoning ) , Goguryeo ' s mangniji ( regent ) Yeon Gaesomun requested that Yi ' nan attack Tang , offering great tributes to him if he did . Yi ' nan , fearful of Tang power , did not do so . ( However , Emperor Taizong was eventually forced to abandon the campaign anyway after being stymied in his siege of Anshi . ) Yi ' nan ' s death and Xueyantuo ' s collapse . Yi ' nan died in 645 . It was described that at this time , Bazhuo , born of Yi ' nan ' s wife , was governing the western part of Xueyantuo , over the Xueyantuo people , while another son of Yi ' nan , Yemang ( 曳莽 ) , who was older but was not born of Yi ' nan ' s wife , was governing the eastern part of Xueyantuo , governing the various tribes . Yemang was said to be violent and disturbed , and also having a bad relationship with Bazhuo . After the funeral , Yemang , fearing that Bazhuo would harm him , left suddenly to return to the eastern part of the khanate . Bazhuo chased him down and killed him , and then took the throne with the title of Jialijulixueshaduomi Khan ( or Duomi Khan for short ) . Bazhuo , after he took the throne , decided to attack Tang , believing that with Emperor Taizong then on campaign against Goguryeo , that Tang borders would be undefended . However , Emperor Taizong , anticipating the possibility of a Xueyantuo attack , had had the general Zhishi Sili ( 執失思力 ) command Tujue soldiers to defend Xia Prefecture ( 夏州 , roughly modern Yulin , Shaanxi ) . Once Bazhuo attacked , Zhishi Sili and another general , Tian Renhui ( 田仁會 ) , set a trap to induce Bazhuo to attack Xia Prefecture , and dealt him a defeat once he was at Xia Prefecture . Bazhuo withdrew , but soon attacked Xia Prefecture again . Briefly after new year 646 , Emperor Taizong ordered , in addition to Zhishi and Tian ' s troops , for troops to be mobilized under the generals Li Daozong the Prince of Jiangxia , Xue Wanche ( 薛萬徹 ) , Ashina She ' er ( 阿史那社爾 ) , Song Junming ( 宋君明 ) , and Xue Guwu ( 薛孤吳 ) , to defend against Bazhuo ' s attack , which Bazhuo called off after reaching the Great Wall and realizing that Tang forces had been mobilized . In turn , in spring 646 , Zhishi and Qiao Shiwang counterattacked , defeating Bazhuo and forcing him to flee , throwing Xueyantuo into a state of confusion . Meanwhile , it was said that Bazhuo was intolerant and ill - tempered , as well as suspicious . He removed Yi ' nan ' s chief advisors and replaced them with people close to him , which led to the nobles despising him — and he responded by killing a large number of them , throwing the Xueyantuo court into terror . Yaoluoge Tumidu ( 藥羅葛吐迷度 ) , the chieftain of Huige , then a Xueyantuo vassal , rebelled along with the Pugu ( 僕骨 ) and Tongluo ( 同羅 ) tribes and dealt Bazhuo a great defeat . Emperor Taizong took the chance to order a major assault against Xueyantuo proper by Li , Ashina , Zhishi , Qibi Heli , Xue Wanche , and Zhang Jian . As the assault was beginning , by chance a Tang officer , Yuwen Fa ( 宇文法 ) , was serving as an emissary to the Wuluohu ( 烏羅護 ) and the Mohe and returning toward Tang , when he encountered the Xueyantuo general Abo ( 阿波 ) . Yuwen attacked Abo with the Mohe troops with him at the time and defeated Abo — which led to even greater confusion for Xueyantuo , whose people believed that the main Tang army had already arrived . In panic , Bazhuo fled to the vassal Ashide ( 阿史德 ) tribe , and when Huige forces heard this , they attacked and killed Bazhuo , slaughtering the Xueyantuo imperial clan members that they could find . Many Xueyantuo generals surrendered to Tang . The remaining Xueyantuo people briefly supported Yi ' nan ' s nephew Duomozhi as Yitewushi Khan to try to revive Xueyantuo , but neither Tang nor the Chile tribes welcomed this development , and Emperor Taizong sent Li Shiji with an army toward Duomozhi ' s location — with the instruction to accept Duomozhi ' s surrender if he wanted to surrender , and to attack if Duomozhi did not . Li Shiji soon arrived at the Khangai , and Duomozhi ' s assistant Tizhen ( 梯真 ) surrendered . Duomozhi fled to the south into the canyon . Li Shiji sent his subordinate Xiao Siye ( 蕭嗣業 ) to comfort him , and he surrendered to Xiao . Not all of his subordinates were willing to surrender , however , and Li Shiji attacked them , killing and capturing many of them . Duomozhi was taken to the Tang capital Chang ' an and made a Tang general , and Xueyantuo was at its end .