 Meanwhile, with certain prefectures north of the Yellow River having submitted to either Tang or Zheng, he carried out a campaign to capture them over the next several months, and was largely successful.By fall 619, Li Shentong, responsible for the Tang operations in the area, had been forced to withdraw to Liyang (黎陽, in modern Hebi, Henan), to join forces with another Tang general, Li Shiji (a former follower of Li Mi).In winter 619, while proceeding toward Wei Prefecture (衛州, roughly modern Xinxiang, Henan), he was ambushed by Li Shiji, and, in anger, he attacked Liyang, capturing it as well as Li Shentong, Li Shiji's father Li Gai (), Wei Zheng, and Emperor Gaozu's sister Princess Tong'an.