Emperor Gaozu of Tang - Struggle Between Sons and The Incident at Xuanwu Gate

Struggle Between Sons and The Incident At Xuanwu Gate

In spring 622, Li Shimin defeated Liu Heita, forcing him to flee to Eastern Tujue, but Liu Heita soon returned with Eastern Tujue reinforcements and killed Emperor Gaozu's nephew Li Daoxuan (李道玄) the Prince of Huaiyang in battle, again seizing former Xia territory, although by this point Li Shimin and Li Yuanji had also defeated Xu Yuanlang and reduced his territory to a few cities.

Meanwhile, an intense rivalry had developed between Li Jiancheng and Li Shimin, as while Li Jiancheng had some contributions toward Tang's reunification of China, Li Shimin had been the one defeating and capturing the major rivals Xue Rengao, Liu Wuzhou, Dou Jiande, and Wang Shichong, causing him to possess the greater reputation among the army. Li Yuanji, who was also often relied on by Emperor Gaozu as a general, supported Li Jiancheng in this rivalry, and often pushed Li Jiancheng toward a more hardline position against Li Shimin, wanting to be crown prince when Li Jiancheng would become emperor. Li Jiancheng and Li Yuanji had better relations with Emperor Gaozu's favored young concubines than Li Shimin did (as their mother Duchess Dou had died before Tang's establishment), and those concubines helped rehabilitate Li Jiancheng's standing before Emperor Gaozu, causing him to no longer consider making Li Shimin crown prince instead, as he considered at one point.

By winter 622, Liu Heita posed the only remaining major threat against Tang rule. At the suggestion of his staff members Wang Gui and Wei Zheng, who argued that Li Jiancheng needed some victories himself to establish his reputation, Li Jiancheng volunteered to command the army against Liu Heita. Emperor Gaozu thus sent Li Jiancheng, assisted by Li Yuanji. Around the new year 623, with Liu's forced bogged down while attacking Tang's Wei Prefecture (魏州, in modern Handan, Hebei), Li Jiancheng and Li Yuanji engaged him at Guantao (館陶, in modern Handan as well), crushing him. Liu fled north toward Eastern Tujue, but was ambushed and captured by his own official Zhuge Dewei (諸葛德威), who delivered him to Li Jiancheng. Li Jiancheng executed Liu. Around the same time, Xu was killed in flight. Meanwhile, Lin Shihong the Emperor of Chu, who had one point controlled modern Jiangxi and Guangdong, had died, and his followers scattered. China was by this point completely unified by Tang except for the domain of Liang Shidu the Emperor of Liang, who controlled modern northern Shaanxi and western Inner Mongolia, although, with Li Fuwei at Chang'an, Fu Gongshi rebelled in 623 and declared himself the Emperor of Song. Fu's rebellion, however, was quelled by Li Xiaogong in 624.

Meanwhile, the rivalry between Li Jiancheng and Li Shimin intensified. In 624, Li Jiancheng requisitioned a number of soldiers from the general Li Yi the Prince of Yan, to supplement his guard corps, against Emperor Gaozu's regulations. When this was revealed to Emperor Gaozu, Emperor Gaozu rebuked Li Jiancheng and exiled his guard commander Keda Zhi (可達志). When, subsequently, Li Jiancheng nevertheless requested the commandant at Qing Prefecture (慶州, in modern Qingyang, Gansu), Yang Wen'gan (楊文幹), to conscript troops, presumably to guard against Li Shimin, the officers Erzhu Huan (爾朱煥) and Qiao Gongshan (橋公山) informed Emperor Gaozu that Li Jiancheng was encouraging Yang to start a rebellion so that they could seize power together. Emperor Gaozu, then at Renzhi Palace (仁智宮, in modern Tongchuan, Shaanxi), was incensed, and summoned Li Jiancheng, then at Chang'an, to Renzhi Palace. Li Jiancheng briefly flirted the idea of occupying Chang'an and not accepting the order, but eventually reported to Renzhi Palace to request forgiveness. Emperor Gaozu put him under arrest. When Yang heard this, Yang rebelled, and Emperor Gaozu, after promising Li Shimin that he would be made crown prince, sent Li Shimin to attack Yang. (Under Emperor Gaozu's promise, Li Jiancheng would be removed as crown prince and created the Prince of Shu instead. He would then send Li Jiancheng to the modern Sichuan region.) Once Li Shimin left, however, Li Yuanji, Emperor Gaozu's concubines, and the chancellor Feng Deyi, all spoke on Li Jiancheng's behalf, and Emperor Gaozu changed his mind, released Li Jiancheng, and allowed him to return to Chang'an and remain as crown prince. Instead, Emperor Gaozu only blamed the discord between his sons on Li Jiancheng's staff members Wang Gui and Wei Ting (韋挺), and Li Shimin's staff member Du Yan, exiling them. Yang was subsequently assassinated by his own subordinates.

Another problem that Emperor Gaozu faced was constant Eastern Tujue incursions. Emperor Gaozu seriously considered burning Chang'an to the ground and moving the capital to Fancheng (樊城, in modern Xiangfan, Hubei), a suggestion that Li Jiancheng, Li Yuanji, and the chancellor Pei Ji agreed with. Li Shimin opposed, however, and the plan was not carried out. Meanwhile, Li Shimin himself 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, but Li Jiancheng and Li Yuanji, after consulting each other, believed that this would only give Li Shimin an opportunity to build up his personal power there, and therefore opposed it. Emperor Gaozu therefore did not carry out the plan.

By 626, Li Shimin was fearful that he would be killed by Li Jiancheng, and his staff members Fang Xuanling, Du Ruhui, and Zhangsun Wuji were repeatedly encouraging Li Shimin to attack Li Jiancheng and Li Yuanji first—while Wei Zheng was encouraging 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 (程知節), from Li Shimin's staff. Zhangsun, who remained on Li Shimin's staff, continued to try to persuade Li Shimin to attack first.

In summer 626, Eastern Tujue was making another attack, and under Li Jiancheng's suggestion, Emperor Gaozu, instead of sending Li Shimin to resist Eastern Tujue as he first was inclined, 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 in Li Yuanji's hands, he would be unable to resist an attack. Li Shimin had Yuchi summon Fang and Du back to his mansion secretly, and then on one night submitted an accusation to Emperor Gaozu that Li Jiancheng and Li Yuanji were committing adultery with Emperor Gaozu's concubines. Emperor Gaozu, in response, issued summonses to Li Jiancheng and Li Yuanji for the next morning, convening the senior officials Pei Ji, Xiao Yu, and Chen Shuda 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 carried out the ambush he had set. He personally fired an arrow that killed Li Jiancheng. Subsequently, Yuchi killed Li Yuanji. Li Shimin's forces entered the palace and, under the intimidation of Li Shimin's forces, Emperor Gaozu agreed to create Li Shimin crown prince, and two months later passed the throne to him (as Emperor Taizong). Li Jiancheng's and Li Yuanji's sons were all executed as well, with Emperor Gaozu not daring to oppose the action.