era name to Wufeng (). Further, at the suggestion of his officials Song Zhengben () and Kong Deshao (), he changed his title to Prince of Xia. Also at this time, Dou surprised and killed another major rebel leader, Wei Dao'er (), who had claimed the title of Emperor of Wei, seizing Wei's forces. He also sent messengers to Luo, trying to persuade Luo to submit. Luo, believing both Dou and Gao Kaidao (who also tried to get him to submit) to be simply bandits, instead submitted to Tang. Dou led his forces against Luo, but could not capture Luo's base at You Prefecture (幽州, converted from Zhuo Commandery) and had to withdraw. Meanwhile, Yuwen, after killing Emperor Yang, had advanced north with Sui's elite Xiaoguo Army (), and he had, after first declaring Emperor Yang's nephew Yang Hao emperor and then poisoned Yang Hao and been several times defeated by Li Mi and then the Tang general Li Shentong (李神通, Emperor Gaozu's cousin), declared himself Emperor of Xu and settled in at Liaocheng (聊城, in modern Liaocheng, Shandong). In spring 619, Dou proclaimed, "I was a Sui subject, and the Sui emperor was my lord. Yuwen Huaji killed my lord, and is therefore my enemy, and I must attack him." He therefore marched on to Liaocheng. Yuwen engaged him outside the city, and Dou defeated him repeatedly, forcing him back into Liaocheng to defend it. Dou put Liaocheng under siege, and the rebel leader Wang Bo (), whom Yuwen had enticed with treasure to help defend the city, opened the city gates and welcomed Dou in. Dou captured Yuwen and formally greeted Emperor Yang's wife Empress Xiao, referring to himself as "your subject." He then carried out a mourning period for Emperor Yang while comforting the Sui officials that had been forced to follow Yuwen. He then executed Yuwen and several of his key associates. He disbanded the large group of Emperor Yang's ladies in waiting that Yuwen had brought along, and disbanded the Xiaoguo Army as well. The Old Book of Tang, while written from Tang's standpoint, praised Dou in this way in the aftermaths of the battle: After this victory, Dou made peace with Wang Shichong and nominally submitted to Yang Tong, the grandson of Emperor Yang who claimed Sui's imperial title at Luoyang after Emperor Yang's death (and whose court was then controlled by Wang Shichong).