Li Jiancheng
In 624, Li Jiancheng requisitioned a number of soldiers from the general Li Yi, the Prince of Yan, to supplement his guard corps. This was against Li Yuan's regulations. Li Yuan rebuked Li Jiancheng when he found out, and exiled his guard commander Keda Zhi (可達志). Nevertheless, Li Jiancheng later 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 Li Yuan that Li Jiancheng was encouraging Yang to start a rebellion so that they could seize power together. Li Yuan, 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 with the idea of occupying Chang'an instead of accepting the order, but eventually reported to Renzhi Palace to request forgiveness. Li Yuan put him under arrest. When Yang heard this, Yang rebelled, and Li Yuan sent Li Shimin to attack Yang. Li Yuan promised Li Shimin that he would replace Li Jiancheng as crown prince, and that Li Jiancheng would be sent to the modern Sichuan region as the Prince of Shu. After Li Shimin left, however, Li Yuanji, Li Yuan's concubines, and the chancellor Feng Deyi, all spoke on Li Jiancheng's behalf, and Li Yuan changed his mind, released Li Jiancheng, and allowed him to return to Chang'an as crown prince. Li Yuan then 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.