Yang Tong, in accordance with Dou's own title, created him the Prince of Xia. Meanwhile, Dou incorporated many key Sui officials into his government, particularly entrusting Pei Ju with reorganizing his government in the form of an imperial one. Independent reign as Prince of Xia In summer 619, Wang Shichong had Yang Tong yield the throne to him, ending Sui and establishing a new state of Zheng. In response, Dou cut off relations with Wang, and began to take on imperial style in his edicts and ceremonies, although he was still using the title of Prince of Xia and not emperor. (It might have been at this time that his wife Lady Cao assumed the title of empress.) He created Emperor Yang's infant grandson Yang Zhengdao the Duke of Xun, and gave Emperor Yang the posthumous name of Min. He entered into an alliance with the Eastern Turks (Dongtujue)'s Shibi Khan Ashina Duojishi, and at the request of Ashina Duojishi's wife, Sui's Princess Yicheng, he delivered Empress Xiao and Yang Zhengdao, as well as the head of Yuwen Huaji, to her. 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. Li Shiji was able to escape, but several days later returned and surrendered to Dou, because Dou had captured Li Gai. Dou made Wei Zheng a staff member, while still letting Li Shiji guard Liyang, but holding Li Gai as hostage, as well as Li Shentong and Princess Tong'an, but treating them with respect and care. He moved his capital from Leshou to Ming Prefecture (洺州, roughly modern Handan, Hebei). By this point, the territory north of the Yellow River and east of the Taihang Mountains were largely his, save for those under the control of Luo Yi (who had