In 1392, Zhu Yuanzhang's heir Zhu Biao, who had been cultivated for many years, died of illness, and Old Zhu was very sad, and then he made a surprising decision, directly ignoring his sons and making his grandson Zhu Yunjiao the crown prince, which can be said to have set a precedent in history, so what made Zhu Yuanzhang make this decision?

To compensate for the eldest son
Zhu Biao was Zhu Yuanzhang's first son, carrying all of Zhu Yuanzhang's hopes, but now he died young, out of his thoughts and compensation for Zhu Biao, Zhu Yuanzhang decided to choose an heir from his sons, and Zhu Yunjiao was a good choice.
Zhu Yunjiao has been clever and clever since childhood, and is deeply loved by his grandfather. Before his father's death, Zhu Yunjiao took good care of Zhu Biao in front of the sickbed, which can be described as filial piety. Zhu Yuanzhang also saw this and decided to pass the throne to Zhu Yunjiao.
The people of the world need benevolent kings
After the establishment of the Ming Dynasty, Zhu Yuanzhang went on a killing spree, frantically eradicating the heroes of the founding of the country, and slaughtering corrupt officials and corrupt officials, in order to remove the obstacles to imperial power and lay the foundation for future generations.
In his later years, Zhu Yuanzhang also understood that slaughter was not a good means of rule, what the world needed more was a benevolent monarch, sons followed themselves to the battlefield, advocating force, and they were likely to continue their brutal rule after they ascended to the throne; and Zhu Yunjiao was kind and benevolent, and he must be able to treat the people well and make the world rule.
To avoid civil unrest
Zhu Yuanzhang quickly identified Zhu Yunjiao as his heir, mainly to avoid civil unrest in the Ming Dynasty.
Crown Prince Zhu Biao sat in the Eastern Palace for many years, and the ministers of the court supported the crown prince, and if he hastily changed his other sons to crown princes, it would not only violate the previous will to divide them into princes, but also met with strong opposition. At this time, pushing the boat along the water and making Zhu Yunjiao the crown prince is the best choice.
Of course, Zhu Yuanzhang's choice of Zhu Yunjiao as his heir is also unjustified in his own right. Zhu Yunjiao was born to the concubine Lü Shi, that is to say, Zhu Yunjiao was the grandson of Shu Chu, and Zhu Di was the son of Shu Chu, and according to the generation, Zhu Di was more qualified to inherit the throne, which can only be said to be Zhu Yuanzhang's eccentricity.
Zhu Yuanzhang's operation also brought trouble to Zhu Yunjiao. After Zhu Yunjiao ascended to the throne, because of his status, he was anxious to cut the domain and prove his legitimacy, which angered Zhu Di and led to the Subsequent Battle of Jingnan. Unfortunately, history has no ifs.