Li Jiancheng
Meanwhile, the rivalry between Li Jiancheng and Li Shimin intensified. In 624, Li Jiancheng requisitioned a number of soldiers from the general Li Yi the Prince of Yan, to supplement his guard corps, against Emperor Gaozu's regulations. When this was revealed to Emperor Gaozu, Emperor Gaozu rebuked Li Jiancheng and exiled his guard commander Keda Zhi (). When, subsequently, Li Jiancheng nevertheless requested the commandant at Qing Prefecture (, in modern Qingyang, Gansu), Yang Wen'gan (), to conscript troops, presumably to guard against Li Shimin, the officers Erzhu Huan () and Qiao Gongshan () informed Emperor Gaozu that Li Jiancheng was encouraging Yang to start a rebellion so that they could seize power together. Emperor Gaozu, then at Renzhi Palace (, in modern Tongchuan, Shaanxi), was incensed, and summoned Li Jiancheng, then at Chang'an, to Renzhi Palace. Li Jiancheng briefly flirted the idea of occupying Chang'an and not accepting the order, but eventually reported to Renzhi Palace to request forgiveness. Emperor Gaozu put him under arrest. When Yang heard this, Yang rebelled, and Emperor Gaozu, after promising Li Shimin that he would be made crown prince, sent Li Shimin to attack Yang. (Under Emperor Gaozu's promise, Li Jiancheng would be removed as crown prince and created the Prince of Shu instead. He would then send Li Jiancheng to the modern Sichuan region.) Once Li Shimin left, however, Li Yuanji, Emperor Gaozu's concubines, and the chancellor Feng Deyi, all spoke on Li Jiancheng's behalf, and Emperor Gaozu changed his mind, released Li Jiancheng, and allowed him to return to Chang'an and remain as crown prince. Instead, Emperor Gaozu only blamed the discord between his sons on Li Jiancheng's staff members Wang Gui and Wei Ting (), and Li Shimin's staff member Du Yan, exiling them. Yang was subsequently assassinated by his own subordinates.