The Yang Wengan incident was a very famous event in the early Tang Dynasty, and it was also a very critical event, because it directly led to the change of XuanwuMen.
As for the Yang Wengan incident, the Zhengshi (specifically, the Old Book of Tang and the New Book of Tang) describes it as follows: The crown prince Li Jiancheng repeatedly plotted to kill Li Shimin, the king of Qin, and he finally decided to take the risk in a desperate manner.
In June of the seventh year of WuDe, he took advantage of the opportunity of Li Yuan to take Shimin and Yuan Ji to Renzhi Palace for summer vacation, colluded with his sworn enemy Yang Wengan, the governor of Gyeongju, and asked Yang Wengan to recruit Xiao Yong for himself and plot a coup d'état.
As a result, Erzhu Huan and Qiao Gongshan, who were responsible for sending armor to Yang Wengan, took the initiative to report this matter to Li Yuan under extreme fear, and Li Yuan, who was angry and afraid, hurriedly summoned Li Jiancheng to see him, and Li Jiancheng, whose plot was exposed, had to come and confess his mistake.
At the same time, Li Yuan also sent an emissary Yuwen Ying to Yang Wengan to summon him to see him, and Yang Wengan, seeing that the matter had been exposed, launched a long-planned mutiny.
In order to quell the rebellion, Li Yuan promised that as long as Li Shimin quelled the rebellion, the future crown prince would be his, and later, Yang Wengan was defeated and killed, but under the hoodwinkle of the princelings, the dim-witted Li Yuan once again fooled Li Shimin and forgave the bold Li Jiancheng.
But is this really the case?
Let's first look at the events:
In June of the seventh year of Tang Wude (624), Gaozu Li Yuan went to Renzhi Palace in Yijun County, north of Chang'an, to take a summer vacation, ordered Li Shimin and Li Yuanji to accompany him, and Li Jiancheng stayed behind to guard the Beijing Division, and suddenly, he received a secret report, and the crown prince Li Jiancheng secretly communicated with Yang Wengan, the governor of Qingzhou, and was raising ordnance to rebel.
Li Yuan was furious and ordered his men to summon Li Jiancheng to renzhi Palace for other reasons, but Li Jiancheng was terrified, and some of his subordinates advised him to raise an army in the city, and others advised him to go alone and plead guilty.
Li Jiancheng obeyed the latter, and as soon as he saw his father, he fell to the ground and worshipped, hitting his head on the ground and almost fainting. Li Yuansheng was furious and detained Li Jiancheng, giving him only rough food.
Li Yuan asked Yang Wengan to visit him, but unexpectedly, the person who passed the order told Yang Wengan about Li Yuan's knowledge of the conspiracy, and Yang Wengan immediately raised an army.
On the one hand, Li Yuan sent people to fight, on the other hand, he summoned Li Shimin to discuss countermeasures, and insisted that Li Shimin personally conquer and suppress, promising to return to the dynasty after victory, deposing the crown prince and establishing Li Shimin instead, seeing that his father said so, Li Shimin led the army to go on the expedition, and as a result, the army had not yet arrived, Yang Wengan's army had collapsed, and Yang Wengan died at the hands of his subordinates.
However, Gaozu did not keep his promise. Still ordering the crown prince to return to Beijing, he only blamed his brothers for discord, but blamed Wang Jue, Wei Ting, and Du Yan of the Prince's Palace of Qin, and exiled them.
This incident was originally a rebellion by the prince, but the result was "brotherly discord"; Li Shimin originally led troops to suppress the rebellion, but was punished by his subordinates being exiled.
Is it that Li Yuan is too dim-witted and trusts the prince too much, or is there something wrong with the record itself? In the Tang Dynasty, a man named Liu Biao wrote a "Sui Tang Jia Dialect", which contained the sentence "People Falsely Sue the Eastern Palace", which Sima Guang quoted when he wrote the Zizhi Tongjian, indicating that there are other accounts of this incident.
Some people made bold speculations based on Liu Biao's remarks: The so-called "Yang Wengan Incident" was originally a conspiracy planned by Li Shimin.
It was true that Li Jiancheng sent Jia Jia to Yang Wengan, but it was not a rebellion, but to strengthen the strength of his cronies and resist the power of the King of Qin.