now taken the name Li Yi, having been granted the imperial surname of Li by Tang's Emperor Gaozu) and Gao Kaidao. In winter 619, Li Shiji considered fleeing to Tang territory, but was fearful that Dou would execute his father Li Gai, and therefore attacked Zheng to gain Dou's trust. In one of the battles against Zheng, Li captured the Zheng army officer Liu Heita, whom Dou was impressed with and created the Duke of Handong. Liu became a trusted general of Dou's, and was often in charge of making surprise attacks and conducting surveillance missions. Around the new year 620, Li Shiji further suggested to Dou that they should attack Cao () and Dai () Prefectures (together making up about modern Heze, Shandong), then controlled by the agrarian leader Meng Haigong () and nominally submitting to Zheng. Li Shiji was planning to ambush Dou as soon as he crossed the Yellow River, but Dou was delayed by Empress Cao's giving birth. Meanwhile, Li Shiji's ally Li Shanghu () could not wait, and ambushed Empress Cao's brother Cao Dan (), but was not able to kill Cao. Li Shiji, hearing the news, fled to Tang territory. When the Xia officials requested that Li Gai be executed, however, Dou stated, "Li Shiji was a Tang subject whom we captured, and he did not forget his former lord. He is a faithful man. What crime has his father committed?" He thus spared Li Gai. He soon defeated and killed Li Shanghu. It was described that by this point, Dou was encouraging his people to farm, and that his realm was peaceful, without banditry, and that merchants and travelers were comfortable enough to spend the night in the wilderness. In summer 620, Dou made another attack on Li Yi, but again could not capture You Prefecture. Meanwhile, his general Wang Fubao (), one of his most capable generals, were being despised by other generals jealous of his talent. They therefore falsely accused him of treason, and Dou executed him. It was said that thereafter, Dou began to suffer more and more military defeats. In fall 620, Tang's Emperor Gaozu sought peace with Xia. Dou agreed to the peace proposal, and sent Princess Tong'an back to Tang, although he continued to hold Li Shentong. In winter 620, he made another attack on Li Yi but again failed to capture You Prefecture. Also around this