Xuanwu Gate Incident - Background

Background

After the founding of the Tang Dynasty, Li Jiancheng was created the heir apparant. Even though Li Jiancheng was designated as the heir apparent, he was often overshadowed by his younger brother Li Shimin. Li Shimin was instrumental in defeating Tang's major rivals. He had led the attack on Dou Jiande and Wang Shichong, whom he defeated in battle, which gained him prestige amongst his contemporaries. Meanwhile, Li Jiancheng was stationed along the northern frontier to guard it against the Tujue, which left him unable to build up a similar reputation. Eventually, Emperor Gaozu elevated Li Shimin's position above all the other nobility. He also placed Li Shimin in charge of the civil and military administration of the eastern plain with Luoyang as its headquarter. There, Li Shimin established himself and appointed about fifty civil and military officials, which made it possible for him to challenge the heir apparent's pre-eminence. In 621, he established the College of Literary Studies with a staff of eighteen scholars to serve as his advisors on state affairs. This may have brought forth the suggestion that Li Shimin could harbor the ambition to ascend to the throne of the Tang empire. Henceforth, Li Jiancheng attempted to undermine Li Shimin by getting his staff members removed and reassigned to other posts.

Prince Li Shimin found himself unable to gain support in the capital Chang'an or inside the palace as he was often away on military expeditions. For his support, he relied on Luoyang where he could successfully build strong support among military and civil officials. Meanwhile in Chang'an, Crown Prince Li Jiancheng was increasing his power by recruiting more than two thousand men to serve in the Changlin troops, which he stationed at the East Palace (東宮) near the Changlin Gate. He was also allied with his second younger brother Prince Li Yuanji. They had the support of Emperor Gaozu's consorts, who often interceded with court affairs on behalf of the two princes.

There were allegations that Yang Wen'gan (楊文幹) was raising troops, so Li Jiancheng—who was left in charge of the capital while Emperor Gaozu was away in his summer palace—could commit a coup for the Tang Dynasty throne. Although, there is still a matter of dispute on whether Li Jiancheng was actually involved amongst historians. Yang Wen'gan was the regional commander of Qingzhou (慶州) in Gansu and a former guard of Li Jiancheng at the East Palace. However, the forementioned plot was disclosed to the authorities. Li Jiancheng was summoned from Chang'an and Yang Wen'gan was summoned from his garrison post. Li Jiancheng went to seek forgiveness against the advice of a subordinate to seize the throne. However, Yang Wen'gan rebelled in the 6th month of 624. Emperor Gaozu sent Li Shimin to put down the rebellion, but Yan's own subordinates killed him after the imperial forces arrived at the scene. Emperor Gaozu initially offered Li Shimin the position of heir apperant in light of Yang's rebellion. However, Li Jiancheng's supporters, Li Yuanji, the palace ladies, and Minister Feng Deyi interceded to clear Li Jiancheng from the affair. Thus, Emperor Gaozu allowed Li Jiancheng to remain the heir apperant, but exiled some of Li Jiancheng's advisors and at least one of Li Shimin's staff member.

Prior to the coup, Prince Li Shimin survived a poisoning attempt by his two brothers. According to the Jiu Tangshu, it happened prior to 626, while the Zizhi Tongjian dates it to the 6th lunar month of 626, placing it within three days of the coup. Bingham (1950a) states that the latter interpretation is most probably the one to be incorrect, since the poisoning had rendered Li Shimin seriously ill. Although, it's still disputed when or whether it had happened. Crown Prince Li Jiancheng and Prince Li Yuanji successfully plotted the dismissal of Fang Xuanling and Du Ruhui (Li Shimin's principal advisors) from service. Yuchi Jingde (Li Shimin's general) escaped an assassination attempt, which was ordered by the two princes. Later, he was slandered by the two princes at court and came near execution if it was not for Li Shimin's intercession. By 626, Li Shimin became increasingly worried by his brothers' successful machinations in turning Emperor Gaozu against him and in removing his staff members.