For those who are very interested in Li Zhi and Li Chengqian, the History Encyclopedia editor brings detailed articles for your reference.

Why did Li Shimin pass on the throne to the ninth son of the emperor, Li Zhi, even though he had appointed Li Chengqian as the crown prince? Emperor Taizong of Tang lived for 52 years and reigned for 23 years. Among the emperors of all dynasties in China, he was not considered short-lived, as he was just over 50 years old. According to ancient rules, anyone who did not reach the age of 60 was considered dead. Emperor Taizong of Tang, known for his heroic deeds, personally built a powerful empire, which can be said to be one of the few wise rulers in Chinese history. Established the prosperous era of the Tang Dynasty’s Zhenguan period. Let the Chinese nation make a name for itself in the world. But the heir he carefully cultivated with his own hands disappointed him greatly. The cold warriors who once followed him to conquer the world did not have the strength to shoulder the responsibility of supporting Li Tang. As conservative ministers took the initiative, young Li Zhi was pushed to the forefront. Helpless, Emperor Taizong of Tang appointed Li Zhi as the crown prince, which can be described as “the most intelligent one, ignorant for a while.
According to records, Li Shimin’s original words were as follows: “If I establish Tai, then the position of crown prince can be managed and obtained. Since the Crown Prince has fallen from grace and the feudal lords have been watching, they have both been abandoned and passed down to their descendants as the last law. If Tai is established, then both Cheng Qian and Zhi are incomplete; if Zhi is established, then both Cheng Qian and Tai are safe.” This passage expresses at least two meanings: first, Li Zhi does not compete for the throne, and his moral character is better than that of Li Cheng Qian and Li Tai. Secondly, Li Zhi will protect the safety of his brothers’ lives and also has the ability to do so. This is obviously praising Li Zhi, believing that he not only has the best moral character, but also has good abilities. Transferring the throne to Li Zhi is not a last resort, but the best choice. So how good is Li Zhi’s character?
In fact, shortly after Li Shimin ascended the throne, he appointed his eldest son Li Chengqian as the crown prince. However, this Li Chengqian was stubborn and playful, and did not care about national affairs at all. When he was young, Li Chengqian was bold and reckless, often taking his trusted followers to steal livestock from the common people, and then killing and cooking them. They disguised themselves as Turkic people and went out in groups to snatch cattle and sheep. In the folk world, it is rampant and enjoyable.

The final result was that Li Chengqian’s position as crown prince was abolished, but Li Taifeng’s brilliance was revealed and his character was not low-key enough. So Emperor Taizong of Tang hesitated whether to give him the position of crown prince. At this moment, Emperor Jiuzi Li Zhi, who had been unknown all along, appeared in the sight of everyone. Although Li Zhi is young, he is indeed the son of Empress Changsun, the first wife of Emperor Taizong of Tang. As the legitimate son, he also had the opportunity to compete for the throne. At that time, the young prince was seen by important officials as a gentle and friendly person who did not compete or compete. At that time, the courtiers had witnessed the Xuanwu Gate Incident and the Crown Prince Li Chengqian and others fighting for the throne, and they were really tired of these princes
Our struggle, on the contrary, has a good impression of the generous and kind Li Zhi.
After taking office as emperor, Li Zhi did several beautiful things: firstly, he followed the rules and continued to follow the good policies of the “Zhenguan Governance” and pioneered the “Yonghui Governance”. Secondly, some inappropriate policies of Li Shimin have been adjusted. For example, the Battle of Liaodong and the contributions of various civil engineers. The third is to address the issue of old officials such as Changsun Wuji and Chu Suiliang controlling the court’s politics. The fourth is to eliminate border troubles and turn the Tang Dynasty’s territory into the largest of the entire Tang Dynasty period. Wu has fulfilled Li Shimin’s wish, which is indeed very good for his brothers. Therefore, Li Shimin is also not wrong.