窦建德
Fresh from his crushing victory over Liu Wuzhou, in August 620 Li Shimin, with an army of 50,000 men, began his advance from Shanxi towards Luoyang. The strategic aim of the Tang prince was to capture the Yellow River valley up to the sea, thus separating the territories held by rival regimes in the north (i.e., Dou Jiande) from any allies in the south, particularly after Du Fuwei, a rebel leader who controlled the Huai River area, chose to acknowledge Tang authority.