 In 621, when the Tang dynasty general Li Shimin (later Emperor Taizong) attacked Wang Shichong the Emperor of Zheng, who ruled the modern Henan region, Dou believed that if Tang were able to destroy Zheng, his own Xia state would suffer the same fate, and therefore went to Wang's aid, against the advice of his strategist Ling Jing () and his wife Empress Cao.Li defeated him at the Battle of Hulao, capturing him.Li's father Emperor Gaozu of Tang subsequently put Dou to death.