Struggle for control of lower Yangtze region
Meanwhile, Du was contending for the control of the region with Chen Leng, who took over Jiangdu after Yuwen's departure; Li Zitong, then at Hailing ; and Shen Faxing, then at Piling and who claimed the title of Prince of Liang. In fall 619, Li was sieging Chen at Jiangling, and Chen sought help from both Shen and Du. Shen sent his son Shen Guan with an army to assist Chen, along with Du. However, Li tricked Shen Guan and Du into attacking each other, and neither was able to assist Chen. Li was able to capture Jiangdu, and then defeated Shen Guan in battle. Both Shen Guan and Du withdrew, and Li took over the Jiangdu region. Li declared himself the Emperor of Wu. With Yang Tong's regime having fallen earlier that year when Yang Tong's official Wang Shichong forced Yang Tong to yield the throne to him, ending Sui and establishing a new state of Zheng, Du decided to submit to Tang Dynasty. Emperor Gaozu of Tang commissioned Du as the commandant of He Prefecture and the commander of the forces south of the Huai River. He also continued to have Du hold the title of Prince of Chu.
Meanwhile, in fall 623, Fu, after tricking Wang into surrendering his command and killing him, rebelled, claiming that Li Fuwei had been detained and had secretly ordered him to rise against Tang. Fu soon declared himself the Emperor of Song. In spring 624, Li Fuwei died suddenly -- with official sources suggesting that he was poisoned by the substances he was taking as a part of alchemical exercises, but also, in a veiled manner, leaving open the possibility that he was assassinated on Emperor Gaozu's orders. After Li Xiaogong the Prince of Zhao Commandery, a son of a cousin of Emperor Gaozu, defeated and killed Fu later that year, Li Xiaogong believed Fu's declaration that he was rebelling under Li Fuwei's orders, and therefore reported it to Emperor Gaozu. Emperor Gaozu ordered that Li Fuwei's titles be posthumously stripped, and that his wife and children be arrested and made slaves. After Li Shimin became emperor in 626, he knew that Li Fuwei was not part of Fu's plot, and therefore restored Li Fuwei's titles, released his wife and children, and reburied him with honor, albeit not with the honor due to a prince, but only of a duke.