In the ninth year of Wu De (626), Li Shimin, the King of Qin, launched the famous "Xuanwumen Rebellion", killing the crown prince Li Jiancheng and The Qi king Li Yuanji. After the victory, Li Shimin forgave all the former princes and the old subordinates of the King of Qi, among which the outstanding talents were also promoted and reused, and many of them later entered the picture.
However, there are exceptions to everything, and there is still an old department of Li Jiancheng who died in the early years of Zhenguan, and he was Luo Yi (Li Yi) who openly rebelled in the first year of Zhenguan (627). So after the "Xuanwumen Revolution", why was There only Luo Yi in Li Jiancheng's old department who rebelled?
When the "Xuanwumen Rebellion" broke out, Luo Yijue was made the king of Yan Commandery and served as the general of Tianjie, one of the Twelve Armies of Guanzhong, leading tens of thousands of elite troops to garrison Jingzhou (泾州, in modern Jingchuan County, Pingliang City, Gansu Province). It can be seen that Luo Yi does not want to avenge Li Jiancheng, otherwise he can take advantage of Li Shimin's unstable position to rebel.
After Li Shimin ascended the throne as Emperor Taizong of Tang, he appointed Luo Yi as the Kaifu Yi Tongsan Division (從一品), and sealed 1,200 households. However, at the same time, Tang Taizong carried out large-scale military reform in order to reduce the burden on the people, and the establishment of the Twelfth Army in Guanzhong was cancelled, resulting in Luo Yi, a General of Tianjie, who could not be succeeded.
Emperor Taizong of Tang then introduced the "reduction of feudal kings (reduction of indiscriminate feudal counties that consume huge amounts of state finances)", and Yan Junwang was one of the county kings who were reduced. Tang Taizong's goal of abolishing the Guanzhong Twelfth Army and implementing the "reduction of the king" was to benefit the country and the people, and also harmed the interests of many former members of the Qin Royal Palace.
However, Luo Yi believed that the cancellation of the 12th Army in Guanzhong and the implementation of the "reduction of the crown prince" were Tang Taizong's retaliation against him, Li Jiancheng's old department, and greed and fear eventually turned into antipathy. So Luo Yi rebelled, and as a result, he was easily pacified by several magistrates and his subordinates in less than a month.