Li Jiancheng
Meanwhile, an intense rivalry had developed between Li Jiancheng and Li Shimin, who now carried the title Prince of Qin. Although Li Jiancheng had made contributions towards Tang's reunification of China, Li Shimin had defeated a number of the most important contenders including Xue Rengao, the Emperor of Qin, Wang Shichong, the Emperor of Zheng, and Dou Jiande, the Prince of Xia. Li Shimin therefore had a stronger reputation in the army. Li Yuanji was also often relied on by Li Yuan as a general and had been created the Prince of Qi. He supported Li Jiancheng in his rivalry with Li Shimin, and often pushed Li Jiancheng toward a more hard-line position, wanting to be crown prince when Li Jiancheng became emperor. Li Jiancheng and Li Yuanji had better relations with Li Yuan's favored young concubines than Li Shimin did (their mother Duchess Dou had died before Tang's establishment), and those concubines helped rehabilitate Li Jiancheng's standing before Li Yuan. Li Yuan had considered making Li Shimin crown prince instead of Li Jiancheng, but his concubines persuaded him not to.