At the beginning of the T'ang dynasty (618--907), the Prince of Ch'in, son of the dynastic founder and later an emperor himself, was engaged in a campaign against some still rebellious warlords in Hopei.
王世充是隋朝遺臣，驍勇善戰，據洛陽自立為帝，派他的姪子王仁則守對外通路轅州城。兩軍交戰，李世民不愧是雄才武略，打得王世充節節敗退；但王世充也非省油的燈，眼見大勢不妙，不惜與原來的死敵﹘﹘據河北自立的竇建德談和。