In May 618, Li Yuan proclaimed himself emperor in Chang'an and established the Tang Dynasty, which was the first year of Wude. Soon after the establishment of the Tang Dynasty, there was a fierce struggle between Li Shimin, the king of Qin, and Li Jiancheng, the crown prince, for the throne.

With the establishment of the Tang Dynasty, Li Shimin worked hard and made great contributions, recruited famous generals such as Wei Chi Jingde, Qin Shubao, and Li Jing, and made extensive friends with well-known people, and his power was unparalleled. Because Li Jiancheng has the legal identity of the crown prince, a large number of imperial relatives gathered around him, and because he stayed in Guanzhong for a long time, he has a solid foundation in the capital Chang'an, and the defenders of the palace (the guards of Xuanwumen) are under his control.

Later, the battle for the crown became more and more intense, and Li Jiancheng and Li Yuanji co-opted Li Yuan's favorite concubines in the palace to slander and frame Li Shimin, but fortunately they were resolved by the idea of the eldest grandson of King Qin. It was even designed to let Li Shimin drink poisoned wine, but fortunately he was saved by Li Yuan's brother Li Shentong, the king of Huai'an.

One day in the ninth year of Tang Gaozu Wude (626 AD), Li Shimin went to the court to accuse Li Jiancheng and Li Yuanji, exposing them for colluding with concubines and misbehaving. Li Yuan was taken aback and said that he would interrogate him personally. That night, Li Shimin dispatched troops.

On July 2, 626 AD, Li Shimin personally led the eldest grandson Wuji and others to ambush near the Xuanwu Gate. The general guarding the Xuanwu Gate is called Chang He, who turned out to be Li Jiancheng's confidant, but he has been bought by Li Shimin. Li Jiancheng and Li Yuanji walked to the Linhu Palace, found that the situation was abnormal, and immediately turned their horses' heads and ran towards the East Palace, only to hear someone shouting: "Prince, King Qi, why don't you go to the court?" Li Yuanji looked back and saw that it was his opponent Li Shimin, he hurriedly took a bow and arrows, and fired three arrows at Li Shimin in a row, but they didn't hit. Li Shimin aimed at Li Jiancheng and shot an arrow back, Li Jiancheng fell off his horse and lost his breath, Li Yuanji hurriedly fled west, and was killed by an arrow shot by Wei Chi Jingde.

When the three brothers were merging, Tang Gaozu was taking his ministers and concubines to take a boat ride in the sea pool. Suddenly, I saw Wei Chi Jingde hurriedly come to report: "The crown prince and the king of Qi are in rebellion, and the king of Qin is afraid that he will alarm His Majesty, so he will send a minister to escort him." Gao Zu was taken aback and hurriedly asked, "Where are the crown prince and King Qi now?" Wei Chi Jingde said: "I have been killed by the King of Qin."

Gao Zu was very sad, ordered the cruise ship to dock, turned back to Pei Lin and the others, and said, "I didn't expect such a thing to happen today, what do you think?" Xiao and Chen said: "Jiancheng and Yuanji have no great merit, and the King of Qin has made great merits and won the hearts of the people, so he should be established as the prince." Wei Chi Jingde hurriedly said: "It is not completely calm outside, please Your Majesty issue an edict that all armies should be under the command of King Qin." Gaozu immediately sent a decree to end the coup.

Immediately afterwards, Li Shimin killed all the wives and concubines of Li Jiancheng and Li Yuanji in front of his father, that is, his nephews and nieces, and Li Yuan's grandchildren.

Three days later, Li Yuan, the greatly stimulated Tang Gaozu, announced that the king of Qin would be appointed as the crown prince, and all major state affairs would be handled by the crown prince. In August of this year, Tang Gaozu Li Yuan was forced to abdicate and proclaimed himself Emperor Taishang. Li Shimin became the emperor, that is, Taizong of the Tang Dynasty, and in the second year, in 627 AD, he changed the name of the year to Zhenguan, and began the prosperity of Zhenguan in the Tang Dynasty. History calls this coup the "Xuanwumen Change".