In ancient times, when the throne was passed on, almost always followed the patriarchal principle of "eldest son". Li Shimin had fourteen sons, and the second Li Chengqian was not only the eldest son of Empress Dowager Yuangong, but also the eldest son. According to this, he was undoubtedly the first heir to the throne after Li Shimin. Unfortunately, Li Chengqian was indisputable among his fourteen sons, and after he became an adult, his personality changed greatly, he coveted pleasure and did not want to enter, and in the end, he became more and more unenterprising and also derived more bad habits, and finally completely hurt Li Shimin's heart.
Later, Li Shimin's attention began to focus on his second son, Li Tai. Because compared with Li Chengqian, Li Tai is a well-behaved baby in his eyes, "intelligent and brilliant, elegant and good literature", positive and enterprising. He was able to write well at a young age, and his appreciation of calligraphy and painting was outstanding among his peers.
In 641 AD, Li Tai wrote the book "Chronicle of the Land", which made Li Shimin even more fond of him. At this time, Li Chengqian, who heard the news, was worried that his position as crown prince was not secure, so he planned to join forces with Hou Junji, Li Yuanchang and others in 642 AD to plot to replicate the "Xuanwumen Incident" and intend to force the palace to seize power. Unfortunately, the matter was exposed, and Prince Li Chengqian could not do it, so after he was deposed, the position of prince was always hanging high, and the minister always let Li Shimin choose the crown prince, and the person who was most in line with him at that time was Li Tai, because he worked hard to govern, and he did his own things very well and was deeply loved by the people. Therefore, according to normal development, Li Tai should be able to get the position of prince. However, the position of prince in the back was indeed a weak Li Zhi.
Li Tai, why do I get so much support from people, or can't I? The reason was that he said a word to Li Shimin, saying that he could be Li Shimin's true son today, and that he would kill his own son in the future and then give the throne to his brother. At such a moment when he thought he was, he expressed his gratitude and loyalty very well. Who knew that in his heart, it became the reason why Li Shimin did not want to give him the position of prince. Why Li Chengqian killed him was because the two brothers did not get reasonable favor.
Therefore, in order to avoid such a brotherly dispute from happening again, Li Shimin chose Li Zhi. Li Zhi, the King of Jin, knew filial piety, and was born from the eldest grandson empress, although he was cowardly and young, it was difficult to be a big thing. However, if he had the teachings of the ministers in the future, it was inevitable that he would not become a good king, and if he thought that if Li Tai changed his position in the future, he could give him the throne again, but unfortunately Li Tai was overwhelmed by the victory he thought was coming, and he actually went to intimidate Li Zhi in two days. Therefore, Li Shimin saw that Li Tai was in the same situation and gave Li Zhi the position of crown prince.