Li Yi
In 622, with Li Shimin attacking Liu, Li Yi led his forces to join Li Shimin to attack Liu's capital at Ming Prefecture (洺州, in modern Handan, Hebei). After the armies stalemated for several months, Li Shimin defeated Liu by using the waters of the nearby Ming River to drown Liu's army, forcing Liu to flee to Eastern Tujue. Li Yi returned to his post at Youzhou. Late that year, however, Liu returned with Eastern Tujue aid, and Li Yi was unable to repel him, although Liu was subsequently defeated by Li Shimin's brother Li Jiancheng the Crown Prince and killed in early 623.