李元吉
After Liu Heita returned from Eastern Tujue and reoccupied old Xia territory, Li Jiancheng, at the suggestion of his staff members Wang Gui and Wei Zheng, volunteered to lead the army against Liu. Emperor Gaozu thus sent Li Jiancheng, assisted by Li Yuanji, against Liu. Around the new year 623, with Liu's forced bogged down while attacking Tang's Wei Prefecture (魏州, in modern Handan, Hebei), Li Jiancheng and Li Yuanji engaged him at Guantao (館陶, in modern Handan as well), crushing him. Liu fled north toward Eastern Tujue, but was ambushed and captured by his own official Zhuge Dewei (諸葛德威), who delivered him to Li Jiancheng. Li Jiancheng executed Liu. China was by this point almost completely unified by Tang. At one point, Li Yuanji tried to persuade Li Jiancheng to have Li Shimin assassinated when Li Shimin was visiting Li Yuanji's mansion, but Li Jiancheng, not having the heart to kill a brother, stopped Li Yuanji from doing so.