Jiancheng

…army under the crown prince Jiancheng at the beginning of 623. The prolonged resistance in Hebei and the comparatively harsh Tang conquest of the region were the beginning of resistance and hostility in the northeast that continued to some degree throughout the Tang dynasty.

…the succession: the crown prince Jiancheng and Li Shimin, the general who had played a large part in the wars of unification. Their rivalry, and the factional strife it generated, reached a peak in 625–626, when it appeared that Jiancheng was likely to succeed. In a military coup, Li Shimin…

…he and his elder brother, Li Jiancheng, were both Tang commanders. Li Shimin distinguished himself as a general and strategist and was largely responsible for the conquest of the eastern capital of Luoyang and the eastern plain. In 621 the emperor delegated to him control of both military and civil…