Li Jiancheng - Participation in Tang's Founding

Participation in Tang's Founding

Even before Li Jiancheng, Li Yuanji, and Chai Shao (who, at the urging of Li Yuan's daughter, left Chang'an on his own while she went into hiding) arrived at Taiyuan, Li Yuan rebelled, declaring that he wanted to support Emperor Yang's grandson Yang You the Prince of Dai, then nominally in charge at Chang'an, as emperor, while honoring Emperor Yang as Taishang Huang (retired emperor). In response, Sui officials arrested Li Zhiyun, took him to Chang'an, and executed him.

Li Yuan made both Li Jiancheng and Li Shimin key generals, and in nine days, they captured Xihe Commandery (西河, roughly modern Lüliang, Shanxi), impressing their father. Subsequently, Li Yuan divided his forces into six armies, having Li Jiancheng and Li Shimin command three each. He also created Li Jiancheng the Duke of Longxi and Li Shimin the Duke of Dunhuang. Subsequently, Li Yuan advanced toward Chang'an, but when he got near to Hedong, his army could not advance due to torrential rains. With rumors running rampant that Liu Wuzhou and Eastern Tujue were about to attack Taiyuan, Li Yuan began ordering a retreat back to Taiyuan; it was only at Li Jiancheng's and Li Shimin's urging (that retreating back to Taiyuan would mean sure defeat) that Li Yuan changed his mind and stayed, and Li Jiancheng and Li Shimin then captured the fortress of Huoyi (霍邑, in modern Linfen, Shanxi), eventually convincing Li Yuan to bypass Hedong and directly advance toward Chang'an. After he crossed the Yellow River into Guanzhong (i.e., the Chang'an region), he sent Li Jiancheng with Liu Wenjing (劉文靜) east to guard Tong Pass and Yongfeng Storage (永豐倉) and to stop any potential Sui reinforcements from the eastern capital Luoyang. Once Li Yuan himself approached Chang'an, he summoned both Li Jiancheng and Li Shimin (whom he had sent north of the Wei River to seize territory) to Chang'an to join him in sieging Chang'an. In winter 617, Li Yuan captured Chang'an and declared Yang You emperor (as Emperor Gong). He had himself created the Prince of Tang, become the regent over Emperor Gong.

In spring 618, Li Yuan sent Li Jiancheng and Li Shimin toward Luoyang, which was then under attack by the rebel leader Li Mi the Duke of Wei, ostensibly to help Sui forces there. The Sui forces at Luoyang rejected the overture, and Li Jiancheng and Li Shimin subsequently returned to Chang'an.

Later in spring 618, Emperor Yang, then at Jiangdu (江都, in modern Yangzhou, Jiangsu), was killed in a coup led by the general Yuwen Huaji. When the news arrived at Chang'an, Li Yuan had Emperor Gong yield the throne to him, establishing Tang Dynasty as its Emperor Gaozu. Emperor Gaozu created Li Jiancheng crown prince.

In 619, Emperor Gaozu sent Li Jiancheng to attack the agrarian leader Zhu Shanhai (祝山海) the Duke of Huxiang, and Li Jiancheng defeated Zhu. Later that year, when Li Gui the Emperor of Liang was captured in a coup by his official An Xinggui (安興貴), who then submitted to Tang, Emperor Gaozu sent Li Jiancheng to welcome An and to escort Li Gui to Chang'an, where Emperor Gaozu executed him.

Meanwhile, Li Jiancheng was developing a reputation for leniency but favoring drinking and hunting. Emperor Gaozu, worried that he was not paying sufficient attention to the important matters of state, had the key ministers Li Gang (李綱) and Zheng Shanguo (鄭善果) join Li Jiancheng's staff.

In fall 620, believing in reports that Li Zhongwen (李仲文), who was then in charge at Taiyuan, was collaborating with Eastern Tujue, was planning to rebel, Emperor Gaozu sent Li Jiancheng to Pufan (蒲反, i.e., Hedong) to guard against Li Zhongwen, while summoning Li Zhongwen back to the capital. Li Zhongwen complied and was subsequently executed.

In spring 621, when the Xiongnu chieftain Liu Xiancheng (劉仚成) harassed Tang's border territory, Emperor Gaozu sent Li Jiancheng to attack Liu. When Li Jiancheng subsequently captured a number of the Xiongnu, he initially released their leaders, leading them to surrender in large numbers, and he then massacred them. Only Liu escaped and fled to Liang Shidu the Emperor of Liang. In 622, Li Jiancheng was one of the commanders that Emperor Gaozu sent, along with Li Shimin, Li Zihe (李子和), and Duan Decao (段德操), to counter an Eastern Tujue incursion.