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Emperor Taizong of Tang


Emperor Taizong of Tang (Chinese: 唐太宗; pinyin: táng tàizōng, January 23, 599 - July 10, 649), personal name Lǐ Shìmín (Chinese: 李世民), was the second emperor of the Tang Dynasty of China, ruling from 626 to 649. Since he encouraged his father, Li Yuan (Emperor Gaozu) to rise against Sui Dynasty rule at Taiyuan in 617 and subsequently defeated several of its most important rivals, including Xue Rengao the Emperor of Qin, Liu Wuzhou the Dingyang Khan, Wang Shichong the Emperor of Zheng, and Dou Jiande the Prince of Xia, he was ceremonially regarded as a cofounder of the dynasty along with Emperor Gaozu,2 This status was confirmed by the founding emperor of Southern Tang Emperor Liezu (Li Bian), who treated Emperors Gaozu and Taizong, as well as his adoptive father Xu Wen, all as founders of his state.3

Tang became the dominant power in eastern Asia in 630, when Emperor Taizong sent his general Li Jing against Eastern Tujue , defeating and capturing its Jiali Khan Ashina Duobi and destroying Eastern Tujue power. Emperor Taizong subsequently took the title of "Heavenly Khan" (天可汗). Throughout the rest of Chinese history, Emperor Taizong's reign was regarded as the exemplary model against which all other emperors were measured, and his "Reign of Zhen'guan" (貞觀之治) was considered one of the golden ages of Chinese history and became required study for future crown princes. During his reign, Tang China flourished economically and militarily. Emperor Taizong was admired for surrounding himself with capable administrators, including the chancellors Fang Xuanling, Du Ruhui, and Wei Zheng, and for listening to their advice and welcoming their criticisms. Emperor Taizong's wife Empress Zhangsun also supported him and served as a capable assistant.4 The greatest praise given to one of his better-regarded successors, Emperor Xuānzong, was the epithet "Little Taizong" (小太宗).5


Li Shimin was born in 599 at Wugong (武功, in modern Xianyang, Shaanxi). His father Li Yuan the Duke of Tang, was a general of the Sui Dynasty and a nephew, by marriage, to Sui's founding emperor Emperor Wen. Li Shimin's grandmother, Duchess Dugu, was a sister of Empress Dugu Qieluo; both were daughters of Dugu Xin (獨孤信), a major general during the dynasty preceding Sui, Northern Zhou. Li Shimin's mother, Duchess Dou, was a daughter of Dou Yi (竇毅), the Duke of Shenwu, and his wife, Princess Xiangyang of Northern Zhou. Duchess Dou bore Li Yuan four sons, Li Jiancheng (an older brother to Li Shimin), and two younger brothers, Li Xuanba (李玄霸, died in 614) and Li Yuanji; and at least one daughter, Princess Pingyang. Li Yuan named Li Shimin "Shimin" as a shortened form of the phrase "save the earth and pacify the people" (濟世安民, jishi anmin). Li Shimin apparently showed talent early in his life, and in 613, the official Gao Shilian, impressed with his ability, gave him a niece (the later Empress Zhangsun) in marriage; he was 14 and she was 12.

In 615, when Emperor Wen's son and successor Emperor Yang was ambushed by Eastern Tujue forces at Yanmen (雁門, in modern Xinzhou, Shanxi), a general call was made for men to join the army to help rescue the emperor. Li Shimin answered that call and served under the general Yun Dingxing (雲定興), apparently with distinction. In 616, when Li Yuan was put in charge of the important city of Taiyuan (太原, in modern Taiyuan, Shanxi), he took Li Shimin there with him, leaving at least three other sons, Li Jiancheng, Li Yuanji, and Li Zhiyun (李智雲, by Li Yuan's concubine Lady Wan), at his ancestral home in Hedong (河東, in modern Yuncheng, Shanxi).

Participation in the Rebellion Against Sui Rule

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Emperor Yang soon became dissatisfied with Li Yuan and Wang Rengong (王仁恭), the governor of Mayi Commandery (馬邑, roughly modern Shuozhou, Shanxi), because they were unable to stop the incursions of the Eastern Tujue and curb the growing strength of agrarian rebels. The Eastern Tujue supported Liu Wuzhou, the Dingyang Khan, who soon rose against Wang, killed him, and captured Emperor Yang's secondary palace near Taiyuan. At that time there had been prophecies throughout the empire that the next emperor would be named “Li,” and Emperor Yang had killed another official named Li Hun (李渾) and his clan over his fears that his nephew Li Min (李敏, the son-in-law of Emperor Yang's sister Yang Lihua, the Princess Leping) might succeed him. Li Yuan became fearful that he and his family might also be executed, and began to consider rebelling against the Emperor.

He was not aware that his son Li Shimin had also been secretly plotting rebellion with Li Yuan's associates Pei Ji and Liu Wenjing. Li Shimin sent Pei to inform Li Yuan of their plans, and to warn Li Yuan that if it were revealed that Li Yuan had consorted with some of Emperor Yang's ladies in waiting at the secondary Jinyang Palace (晉陽宮), which was under Pei's supervision, all of them would be slaughtered. Li Yuan agreed to join them. After secretly summoning Li Jiancheng and Li Yuanji from Hedong, and his son-in-law Chai Shao (柴紹) from the capital Chang'an, he declared a rebellion, under the pretext of supporting Emperor Yang's grandson Yang You, the Prince of Dai, who was nominally in charge at Chang'an, with Emperor Yang at Jiangdu (江都, in modern Yangzhou, Jiangsu), as emperor. He appointed both Li Jiancheng and Li Shimin major generals and advanced southwest, toward Chang'an. Li Yuan also created Li Shimin the Duke of Dunhuang.

When Li Yuan arrived near Hedong, his army became bogged down by the weather. Food supplies were running low, and there were rumors that Eastern Tujue and Liu Wuzhou were about to attack Taiyuan. Li Yuan initially ordered a retreat, but at the insistence of Li Jiancheng and Li Shimin, continued to advance. After defeating Sui forces at Huoyi (霍邑, also in modern Yuncheng), Li Yuan left a small contingent to watch over Hedong and advanced across the Yellow River into Guanzhong (the Chang'an region). He sent Li Jiancheng to capture the territory around the Tong Pass region, to prevent Sui forces at Luoyang from reinforcing Chang'an, and Li Shimin north of the Wei River to capture territory there, while he led his own forces to Chang'an. Meanwhile, Li Shimin's sister (wife of Chai Shao) had also risen in rebellion in support of him, gathered a sizeable army and captured some cities. She joined forces with Li Shimin and her husband, Chai Shao. Li Yuan reconsolidated his forces and put Chang'an under siege. In the winter of 617, he captured Chang'an and placed Yang You on the throne as Emperor Gong of Sui. He had himself made regent (with the title of grand chancellor) and created the Prince of Tang. He created Li Shimin the Duke of Qin.

Li Yuan's control of the Chang'an region was contested almost immediately by the rebel ruler Xue Ju, the Emperor of Qin, who sent his son Xue Rengao toward Chang'an. Li Shimin was sent to resist Xue Rengao, and defeated him at Fufeng (扶風, in modern Baoji, Shaanxi). Xue Ju considered surrendering to Li Yuan, but was dissuaded from doing so by his strategist Hao Yuan (郝瑗).

Most of Sui territory did not recognize Emperor Gong and continued to regard Emperor Yang as the sovereign, not as a retired emperor. In the spring of 618, Sui's eastern capital Luoyang, where the officials in charge did not recognize Li Yuan's authority, was under attack from the rebel ruler Li Mi, the Duke of Wei. Li Yuan sent Li Jiancheng and Li Shimin to Luoyang, ostensibly to aid the Sui forces at Luoyang, but with the intention of discovering whether Luoyang might submit to him. The officials at Luoyang rebuffed his attempt at rapprochement, and Li Jiancheng and Li Shimin, not wanting to fight for control of Luoyang, withdrew. Li Yuan subsequently changed Li Shimin's title to Duke of Zhao.

In the summer of 618, news arrived at Chang'an that Emperor Yang had been killed at Jiangdu in a coup led by the general Yuwen Huaji. Li Yuan made Emperor Gong yield the throne to him, establishing Tang Dynasty and declaring himself Emperor Gaozu. He created Li Jiancheng Crown Prince, but made Li Shimin the Prince of Qin, also appointing him Shangshu Ling (尚書令), the head of the executive bureau of the government (尚書省, Shangshu Sheng), a post similar to that of a chancellor. At the same time, Li Shimin continued to serve as a major general.

During Emperor Gaozu's Reign

The campaign to reunify the empire

Xue Ju attacked Jing Prefecture (涇州, roughly modern Pingliang, Gansu) and Emperor Gaozu sent Li Shimin to resist him. Li Shimin established his defenses and refused to engage Xue, intending to wear down Xue Ju's forces. However, Li Shimin became ill with malaria and let his assistants Liu Wenjing and Yin Kaishan (殷開山) take command, ordering them not to engage Xue Ju. Liu and Yin did not take the threat of Xue Ju seriously, and Xue Ju ambushed them at Qianshui Plain (淺水原, in modern Xianyang), crushing the Tang forces and killing more than half of the troops. Li Shimin was forced to withdraw to Chang'an, and Liu and Yin were removed from their posts. This was the only defeat of Li Shimin documented in historical records until the Goguryeo campaign of 645.

The victorious Xue Ju was prepared to launch an assault on Chang'an itself, at the advice of Hao Yuan, but died suddenly of an illness in the fall of 618 and was succeeded by Xue Rengao. Emperor Gaozu then sent Li Shimin against Xue Rengao. Three months after Xue Rengao took the throne, after a fierce battle between Li Shimin and Xue Rengao's major general Zong Luohou (宗羅睺), Zong's forces were crushed. Xue Rengao withdrew into the city of Gaozhi (高墌, in modern Xianyang), and his soldiers began surrendering to Li Shimin in mass. Xue Rengao was forced to surrender, and Li Shimin had him delivered to Chang'an, where he was executed. Around the New Year in 619, Emperor Gaozu made Li Shimin Taiwei (太尉, one of the Three Excellencies) and put him in charge of Tang operations east of the Tong Pass.

In spring 619, Liu Wuzhou launched a major offensive against Tang. He captured Taiyuan in summer 619, forcing Li Yuanji, who had been in charge there, to flee, and then continued his offensive south. Emperor Gaozu sent Pei Ji against him, but by the winter of 619, Liu had crushed Pei's forces and taken over nearly all of modern Shanxi. Emperor Gaozu considered abandoning the region altogether. Li Shimin offered to lead an army against Liu, and Emperor Gaozu agreed and commissioned him with an army. Li Shimin crossed the Yellow River and approached Liu's major general Song Jin'gang (宋金剛) but did not engage him, choosing to try to wear Song out. He had his subordinates Yin Kaishan and Qin Shubao engage the other Dingyang generals Yuchi Jingde and Xun Xiang (尋相) in relatively low-level engagements. Eventually, in the spring 620, when Liu and Song ran out of food supplies, they retreated, and Li Shimin gave chase, dealing Song a major defeat. Yuchi and Xun surrendered, and Li Shimin pursued Liu and Song until they fled to Eastern Tujue. All of Dingyang territory fell into Tang hands.

In the summer of 620, Emperor Gaozu again commissioned Li Shimin against a major enemy, the former Sui general Wang Shichong, who had made Sui's last emperor, Emperor Yang's grandson Yang Tong, yield the throne to him in 619, establishing a new state of Zheng as its emperor. When Li Shimin arrived at the Zheng capital Luoyang, Wang offered peace, but Li Shimin rebuffed him and put Luoyang under siege, while his subordinates took Zheng cities one by one. By the winter of 620, most of Zheng territory, except for Luoyang and Xiangyang (襄陽, in modern Xiangfan, Hubei), defended by Wang Shichong's nephew Wang Honglie (王弘烈), had submitted to Tang. Wang sought the assistance of Dou Jiande the Prince of Xia, who controlled most of modern Hebei. Dou, reasoning that if Tang were able to destroy Zheng, his own Xia state would be threatened, agreed. He sent an official, Li Dashi, to try to persuade Li Shimin to withdraw, but Li Shimin detained Li Dashi and gave no response. Li Shimin chose some 1000 elite soldiers, clad in black uniform and black armor, commanded by himself, to serve as advance forward troops, with Qin, Cheng Zhijie (程知節), Yuchi, and Zhai Zhangsun (翟長孫) as his assistants.

Battle of Hulao

By the spring of 621, Luoyang was in a desperate situation, and Xia forces had not yet arrived. Luoyang's defenses, aided by powerful bows and catapults, had inflicted serious casualties on the Tang troops. Emperor Gaozu, hearing that Dou had decided to come to Wang's aid, ordered Li Shimin to withdraw, but Li Shimin sent his secretary Feng Deyi to Chang'an to explain to Emperor Gaozu that if he did withdraw, Wang would recover and again be a major threat in the future. Emperor Gaozu agreed and allowed Li Shimin to continue the siege of Luoyang. When the Xia forward troops arrived, Li Shimin surprised and defeated them, and then sent Dou a letter suggesting that he withdraw. Dou refused, and, against the advice of his wife Empress Cao and secretary general Ling Jing (凌敬) that he should instead attack Tang's prefectures in modern southern Shanxi, he marched toward Luoyang.

Anticipating Dou's maneuver, Li Shimin left a small detachment, commanded by Li Yuanji, at Luoyang, while marching east himself, taking up positions at the strategic Hulao Pass. When the armies engaged at Hulao, Li Shimin defeated Dou and captured him. He took Dou back to Luoyang and displayed him to Wang Shichong. Wang, in fear, considered abandoning Luoyang and fleeing south to Xiangyang, but reminded by his generals that Dou had been his only hope, he surrendered. Xia forces, after initially fleeing to the Xia capital in Ming Prefecture (洺州, in modern Handan, Hebei), also surrendered. Zheng and Xia territory were now under Tang control. Li Shimin returned to Chang'an in a grand victory procession, and, as a reward, Emperor Gaozu awarded both him and Li Yuanji three mints so that they could mint money of their own. He also bestowed on Li Shimin the special title of "Grand General of Heavenly Strategies" (天策上將, Tiance Shangjiang). Meanwhile, Li Shimin's staff of generals and strategists, was being supplemented with a number of literary men.

The former Xia territory did not remain in Tang hands for long, as in winter 621, the Xia general Liu Heita rose against Tang rule, claiming to avenge Dou, whom Emperor Gaozu had executed in Chang'an. Liu was allied with Xu Yuanlang, a former agrarian rebel general who was nominally under Wang Shichong and who had submitted to Tang after Wang's defeat. Liu dealt successive defeats to Emperor Gaozu's cousin Li Shentong (李神通) the Prince of Huai'an, Li Xiaochang (李孝常) the Prince of Yi'an, and Li Shiji. Emperor Gaozu sent Li Shimin and Li Yuanji against Liu. In 622, after some indecisive battles with Liu, who had by then taken over almost all of former Xia territory and claimed the title of Prince of Handong, Li Shimin defeated Liu by flooding his army with water from the Ming River (洺水, flowing near Ming Prefecture), and Liu fled to Eastern Tujue. Li Shimin then headed east and attacked Xu, defeating him. After leaving Li Shiji, Li Shentong, and Ren Gui (任瓌) to continue the attack on Xu, Li Shimin returned to Chang'an.

The struggle against Li Jiancheng and Li Yuanji

An intense rivalry arose between Li Shimin and his older brother Li Jiancheng, who had been created Crown Prince in 618, reportedly after Emperor Gaozu first offered the position to Li Shimin as a reward for his contributions. Li Shimin's accomplishments caused people to speculate that he might displace Li Jiancheng as Crown Prince, and Li Jiancheng, an accomplished general himself, was overshadowed by his younger brother. The court became divided into a faction favoring the Crown Prince and a faction favoring the Prince of Qin. The rivalry caused particular problems within capital, because the commands of the Crown Prince, the Prince of Qin, and the Prince of Qi (Li Yuanji) were considered to have the same force as the emperor's edicts, and officials had to carry out conflicting orders, usually acting on the ones that arrived first. Li Shimin had a staff of talented men, but Li Jiancheng was supported by Li Yuanji, as well as Emperor Gaozu's concubines, who had better relationships with Li Jiancheng and Li Yuanji than they did with Li Shimin.

Late in 622, when Liu Heita returned to former Xia domain after receiving aid from Eastern Tujue, defeating and killing Li Shimin's cousin Li Daoxuan (李道玄) the Prince of Huaiyang, he again regained most of former Xia territory. Li Jiancheng's staff members Wang Gui and Wei Zheng suggested that Li Jiancheng needed to enhance his own reputation in battle, and so Li Jiancheng volunteered to march against Liu. Emperor Gaozu sent Li Jiancheng, assisted by Li Yuanji, to attack Liu. Li Jiancheng defeated Liu around the New Year in 623, and Liu was betrayed by his own official Zhuge Dewei (諸葛德威) and delivered to Li Jiancheng. Li Jiancheng killed Liu and returned to Chang'an in triumph. This victory roughly united China under Tang rule.

For the next few years, the rivalry between Li Jiancheng and Li Shimin intensified, although both served as generals when Eastern Tujue made incursions. In 623, when the general Fu Gongshi rebelled at Danyang (丹楊, in modern Nanjing, Jiangsu), Emperor Gaozu briefly commissioned Li Shimin to attack Fu, but soon cancelled the order and sent Li Shimin's cousin Li Xiaogong, the Prince of Zhao Commandery, instead.

In 624, when Li Jiancheng was found to have, against regulations, tried to add soldiers to his guard corps, Emperor Gaozu was so angry that he put Li Jiancheng under arrest. In fear, Li Jiancheng's guard commander Yang Wen'gan (楊文幹) rebelled. Emperor Gaozu sent Li Shimin against Yang, offering to make him Crown Prince on his return. After Li Shimin left, however, Feng Deyi (now a chancellor), Li Yuanji, and the concubines all spoke on Li Jiancheng's behalf, and after Li Shimin returned, Emperor Gaozu did not depose Li Jiancheng. Instead, he blamed the discord between him and Li Shimin on Li Jiancheng's staff members Wang Gui and Wei Ting (韋挺) and Li Shimin's staff member Du Yan, exiling them to Xi Prefecture (巂州, roughly modern Liangshan Yi Autonomous Prefecture, Sichuan).

Later that year, Emperor Gaozu, troubled by repeated Eastern Tujue incursions, seriously considered burning Chang'an to the ground and moving the capital to Fancheng (樊城, also in modern Xiangfan), a suggestion that Li Jiancheng, Li Yuanji, and Pei Ji agreed with. Li Shimin opposed the plan, however, and it was not carried out. Meanwhile, Li Shimin was sending his confidants to Luoyang to build up personal control of the army there. After an incident in which Li Shimin suffered a severe case of food poisoning after feasting at Li Jiancheng's palace, an event that both Emperor Gaozu and Li Shimin apparently interpreted as an assassination attempt, Emperor Gaozu considered sending Li Shimin to guard Luoyang to prevent further conflict. Li Jiancheng and Li Yuanji opposed this plan because they believed that it would only give Li Shimin an opportunity to build up his personal influence in Luoyang, so Emperor Gaozu did not carry it out.

The rivalry continued. According to traditional historical accounts, in one incident, when Li Shimin visited Li Yuanji's mansion, Li Yuanji wanted to assassinate him, but Li Jiancheng, who could not resolve to kill a brother, stopped the plot. There was another incident in which Li Jiancheng deliberately had Li Shimin ride a horse that was known for throwing its riders, causing him to fall off it several times.

By 626, Li Shimin was fearful that he would be killed by Li Jiancheng. His staff members Fang Xuanling, Du Ruhui, and Zhangsun Wuji repeatedly encouraged Li Shimin to attack Li Jiancheng and Li Yuanji first, while Wei Zheng was encouraged Li Jiancheng to attack Li Shimin first. Li Jiancheng persuaded Emperor Gaozu to remove Fang and Du, as well as Li Shimin's trusted guard officers Yuchi Jingde and Cheng Zhijie, from Li Shimin's staff. Zhangsun, who remained on Li Shimin's staff, continued to try to persuade Li Shimin to attack first.

In the summer of 626, Eastern Tujue was making another attack. At Li Jiancheng's suggestion, Emperor Gaozu, instead of sending Li Shimin to resist Eastern Tujue as he had first intended, decided to send Li Yuanji instead. Li Yuanji was given command of much of the army previously under Li Shimin's control, further troubling Li Shimin, who believed that with the army under Li Yuanji's control, he would be unable to resist an attack. Li Shimin had Yuchi secretly summoned Fang and Du back to his mansion. One night, he submitted an accusation to Emperor Gaozu that Li Jiancheng and Li Yuanji were committing adultery with Emperor Gaozu's concubines. In response, Emperor Gaozu, issued summonses to Li Jiancheng and Li Yuanji to come to his palace the next morning, where the senior officials Pei Ji, Xiao Yu, and Chen Shuda would convene to examine Li Shimin's accusations. As Li Jiancheng and Li Yuanji approached the central gate leading to Emperor Gaozu's palace, Xuanwu Gate (玄武門), Li Shimin ambushed them. He personally fired an arrow that killed Li Jiancheng. Yuchi killed Li Yuanji. Li Shimin's forces entered the palace and intimidated Emperor Gaozu into creating Li Shimin crown prince. The sons of Li Jiancheng and Li Yuanji were killed, and Li Shimin took Li Yuanji's wife Princess Yang as a concubine. Two months later, Emperor Gaozu yielded the throne to Li Shimin as Emperor Taizong.

Early Reign

A mural painting of Emperor Taizong (located bottom, center) dated to 642 C.E., located in Cave 220, Dunhuang, Gansu province.

One of the first actions that Emperor Taizong carried out as emperor was releasing a number of ladies in waiting from the palace and returning them to their homes, so that they could be married. He created his wife Princess Zhangsun as empress, and their oldest son Li Chengqian as crown prince.

Emperor Taizong faced a crisis almost immediately, as Eastern Tujue's Jiali Khan Ashina Duobi, along with his nephew the subordinate Tuli Khan Ashina Shibobi (阿史那什鉢苾), launched a major incursion toward Chang'an. Just 19 days after Emperor Taizong took the throne, the two khans were across the Wei River from Chang'an. Emperor Taizong, accompanied by Gao Shilian and Fang Xuanling, was obliged to meet Ashina Duobi across the river and personally negotiate peace terms, including tributes to Eastern Tujue, before Ashina Duobi withdrew.

Late in 626, Emperor Taizong ranked the contributors to Tang rule and granted them titles and fiefs, naming among the first rank of contributors Zhangsun Wuji, Fang, Du Ruhui, Yuchi Jingde, and Hou Junji. When Li Shentong, his distant uncle, objected to being ranked under Fang and Du, Emperor Taizong personally explained how Fang and Du's strategies had allowed him to be successful. This example pacified the others who were objecting to being assigned lower ranks. Emperor Taizong also buried Li Jiancheng and Li Yuanji with the honors due imperial princes and had their staff members attend the funeral processions.

Taizong began to reorganize the government, dismissing his father's trusted advisors Xiao Yu and Chen Shuda, and making his own trusted advisors chancellors. Xiao was soon restored as chancellor, but his career during Emperor Taizong's reign was one of repeated dismissals and restorations. However, he also began to pay careful attention to the officials' submissions and their criticisms of imperial governance, making changes where he saw the need. He also began to trust Wei Zheng in particular, accepting much advice from Wei concerning his personal conduct. He was also willing to demote his own trusted advisors, as he demoted Gao after finding that Gao had held back submissions from his deputy Wang Gui. Viewing Sui's Emperor Yang as a negative example, he frequently solicited criticisms, rewarding those officials, such as Wei and Wang Gui, who were willing to offer them.

In 627, the general Li Yi, Prince of Yan, a late-Sui warlord who later submitted to Tang and had been associated with Li Jiancheng, fearing that Emperor Taizong would eventually take action against him, rebelled in Bin Prefecture (豳州, in modern Xianyang), but was quickly crushed by the official Yang Ji (楊岌) and killed in flight. Later that year, when Emperor Gaozu's cousin Li Youliang (李幼良) the Prince of Changle, the commandant at Liang Prefecture (涼州, roughly modern Wuwei, Gansu), was accused of allowing his staff to oppress the people and to trade with Qiang and Xiongnu tribesmen, Emperor Taizong sent the chancellor Yuwen Shiji (Yuwen Huaji's brother) to investigate. Fearing for their lives, Li Youliang's staff members plotted to hold him hostage and rebel. When this was discovered, Emperor Taizong forced Li Youliang to commit suicide. Late in the year, Wang Junkuo (王君廓), the commandant at You Prefecture (幽州, roughly modern Beijing), also rebelled, but was defeated quickly and killed in flight. When there were reports that Feng Ang (馮盎), a warlord in the modern Guangdong region, was rebelling, Emperor Taizong, at Wei's suggestion, sent messengers to appease Feng, and Feng submitted.

Also in 627, Emperor Taizong, seeing that there were too many prefectures and counties, consolidated and merged many of them, and created another level of local political organization above prefectures-the circuit (道, dao)-dividing his state into ten circuits.

In 628, Ashina Duobi and Ashina Shibobi had a falling out, and Ashina Shibobi submitted to Emperor Taizong, as did the chieftains of Khitan tribes, who had previously submitted to Eastern Tujue. With Eastern Tujue in turmoil, Ashina Duobi was no longer able to protect the last late-Sui rebel ruler who alone remained standing against Tang pressure, Liang Shidu, the Emperor of Liang. In the summer of 628, with the Tang generals Chai Shao and Xue Wanjun (薛萬均) besieging the Liang capital Shuofang (朔方, in modern Yulin, Shaanxi), Liang Shidu's cousin Liang Luoren (梁洛仁) killed Liang Shidu and surrendered, finally uniting China. Eastern Tujue's vassal Xueyantuo broke away from the weakened Eastern Tujue and formed its own khanate, and Emperor Taizong entered into an alliance with Xueyantuo's leader Yi'nan (夷男), creating Yi'nan the Zhenzhupiqie Khan (真珠毗伽可汗, or Zhenzhu Khan).

In late 629, believing the time ripe for a major attack on Eastern Tujue, Emperor Taizong commissioned the general Li Jing with overall command of a multi-pronged army, assisted by the generals Li Shiji, Chai, and Xue Wanche (薛萬徹, Xue Wanjun's brother), to attack Eastern Tujue at multiple points. The army was successful in its attacks, forcing Ashina Duobi to flee, and by late spring of 630, Ashina Duobi had been captured, and Eastern Tujue chieftains had all submitted to Tang. Emperor Taizong spared Ashina Duobi but detained him at Chang'an, as he considered what to do with the Eastern Tujue people. Chancellor Wen Yanbo advocated leaving the Eastern Tujue people within Chinese borders to serve as a defense perimeter, and Chancellor Wei advocated leaving them outside the borders. Emperor Taizong accepted Wen's suggestion and established a number of prefectures to accommodate the Eastern Tujue people, still leaving them governed by their chieftains, without creating a new khan to govern them.

In 631, Emperor Taizong established a feudal scheme, where the contributors to his reign were given, in addition to their current posts, additional posts as prefectural governors, to be passed on to their descendants. This scheme was soon cancelled, however, because of strong opposition from his advisers, particularly from Zhangsun Wuji.

After the conquest of Eastern Tujue, Emperor Taizong's officials repeatedly requested that he carry out sacrifices to heaven and earth at Mount Tai. Emperor Taizong, though tempted by the proposal, was repeatedly dissuaded from doing so by Wei, who pointed out that such an endeavor would impose heavy expenses and labor burdens on the people, and open China's borders to possible attack.

Middle reign

A painting portraying Tang Taizong by painter Yan Liben (c. 600 - 673).

In 634, Emperor Taizong sent thirteen high level officials, including Li Jing and Xiao Yu, to examine the circuits to see whether the local officials were capable, to find out whether the people were suffering, to comfort the poor, and to select capable people to serve in civil service. Li Jing initially recommended that Wei accompany them on the examination, but Emperor Taizong declared that Wei needed to stay to point out his faults, and that he could not afford to have Wei away even for a single day.

Around this time, conflicts were increasing between Tang and Tuyuhun, whose Busabo Khan Murong Fuyun, following the advice of his strategist, the Prince of Tianzhu, had been repeatedly attacking the borders of Tang prefectures. At one point, Murong Fuyun sought to have a Tang princess marry his son Murong Zunwang (慕容尊王), but the marriage negotiations broke down over Emperor Taizong's insistence that Murong Zunwang come to Chang'an for the wedding. In the summer of 634, Emperor Taizong sent generals Duan Zhixuan and Fan Xing (樊興) to lead forces against Tuyuhun, but Duan, while not defeated, could not make major gains against Tuyuhun's highly mobile forces, who avoided direct confrontation. Once Duan withdrew, Tuyuhun resumed hostilities. In winter 634, the Tufan king Songtsän Gampo also made overtures to marry a Tang princess, and Emperor Taizong sent the emissary Feng Dexia (馮德遐) to Tufan to negotiate an alliance against Tuyuhun. In the winter of 634, he commissioned Li Jing, assisted by the other generals Hou Junji, Li Daozong, Li Daliang (李大亮), Li Daoyan (李道彥), and Gao Zengsheng (高甑生), to attack Tuyuhun. In 635, Li Jing's forces crushed the Tuyuhun forces. Murong Fuyun was killed by his own subordinates, and his son Murong Shun killed the Prince of Tianzhu and surrendered. Emperor Taizong created Murong Shun the new khan, and when he was assassinated soon afterward, made Murong Shun's son Murong Nuohebo khan in his place

Also in 635, Emperor Gaozu died, and Emperor Taizong briefly had Li Chengqian serve as regent while he observed a mourning period. When he resumed his authority less than two months later, he continued to authorize Li Chengqian to rule on minor matters.

In the spring of 636, Emperor Taizong commissioned his brothers and sons as commandants and changed their titles in accordance with the commands that they received. He sent them to their posts with the exception of his son Li Tai, Prince of Wei, who by this point was beginning to be highly favored by him. He allowed Li Tai, who favored literature, to engage literary men as assistants. Rumors began to circulate that Emperor Taizong might let Li Tai displace Li Chengqian, his eldest son, who was beginning to lose favor.

In the fall of 636, Empress Zhangsun died. Emperor Taizong mourned her bitterly and personally wrote the text of her monument.

In the summer of 637, Emperor Taizong attempted to establish the feudal scheme that he had considered and abandoned in 631, creating 35 hereditary prefect posts. By 639, however, the system was again abandoned in the face of much opposition.

Sometime before 638, Emperor Taizong, disgusted with the traditional noble clans of Cui, Lu, Li, and Zheng and believing that they were abusing their highly honored names, commissioned Gao Shilian, Wei Ting, Linghu Defen (令狐德棻), and Cen Wenben to compile a work, later known as the Records of Clans (氏族志). It was intended to divide the clans into nine classes based on their past contributions, and good and bad deeds. Gao submitted an initial draft in which he ranked the branch of the Cui clan of the official Cui Min'gan (崔民幹) as the highest, a decision that Emperor Taizong rejected, pointing out that Gao was looking at tradition an