In 1402 AD, Zhu Di, the king of Yan, attacked Yingtian (Nanjing), the capital of the Ming Empire, and Zhu Yunwen, the emperor of Jianwen, disappeared without a trace in the chaos. Zhu Di usurped power and seized the throne as a vassal king, and it took only four years to break the pattern of the country carefully arranged by Zhu Yuanzhang and sit on the throne of the emperor.
Zhu Yuanzhang, the self-made emperor in history, although his background is poor, his ability is undoubted, and his political wisdom is unique in the world, unparalleled. In order to ensure that his son Zhu Biao and grandson Zhu Yunwen can sit firmly in the country, he can be described as painstaking and meticulous planning. However, he did not expect that only four years after his death, the political landscape he had painstakingly managed would be completely overturned by Zhu Di.
Could it be that he really didn't foresee the threat of King Yan? Or is he overconfident that his layout is flawless? How wise Zhu Yuanzhang is, in fact, he had already considered the hidden dangers posed by King Yan before his death, and planned to get rid of his "thorny" son for a long time in his later years.
Among Zhu Yuanzhang's many sons, Zhu Di, the king of Yan, is undoubtedly the most outstanding. But why didn't Zhu Yuanzhang consider passing the throne to him? Regarding the choice of the prince, Zhu Yuanzhang must have been carefully considered. During the lifetime of the eldest son, Zhu Biao, this problem was not prominent. Although Zhu Biao has a soft personality, his talent and ability should not be underestimated, and he is deeply loved and supported by the ministers. He was clearly a benevolent king of tomorrow, and as the eldest of all sons, he also had great prestige among his brothers. Zhu Yuanzhang removed all obstacles for his future path and never doubted his ability to succeed to the throne.
However, Zhu Biao's untimely death brought the question of succession to the throne to the fore. At this time, the best heirs are undoubtedly the eldest grandson Zhu Yunwen and the fourth son Zhu Di. In terms of ability, Zhu Di is undoubtedly outstanding and a talent. But the succession to the throne involves not only personal ability, but also the overall situation of the stability of the entire imperial regime. Therefore, Zhu Yuanzhang must consider it from a macro perspective. 
So, why did Zhu Di fail to become the prince? The factors involved are complex and varied, but in the final analysis, Zhu Yuanzhang's consideration of the stability of the regime transcends personal emotions and expectations.
First of all, Zhu Di ranked fourth, and there were two brothers in front of him, King Qin and King Jin. Although the abilities of these two brothers are mediocre, they each have a heavy army and a powerful side. Since they are all Zhu Di's predecessors and have deep qualifications, if Zhu Di ascends to the throne, they will inevitably be unconvinced, which will undoubtedly lead to the intensification of the struggle between the vassal kings. Such infighting is undoubtedly a major hidden danger to the stability of the empire.
Secondly, in ancient societies, the stability of the imperial throne process can be said to be a crucial cornerstone. Especially for the Ming Empire, this is the first time that it has inherited the throne, and it must be a model of stability and peace, which has important benchmarking significance for the future of the Ming Dynasty. Therefore, the core of the issue of the throne is the stability of the power inheritance. This is not only a guarantee for the future, but also a maintenance of the stability of the entire empire.
Moreover, Zhu Yunwen is the eldest grandson, and he has outstanding advantages in Zongli, plus he is very similar to Zhu Biao, with a benevolent personality, and extremely filial piety, and a good reputation among the courtiers, plus he must be a benevolent monarch who implements a relaxed policy after he succeeds to the throne. Zhu Yuanzhang in the world has already been defeated, and what he needs in the future is naturally the "king of success", and the soft and kind Zhu Yunwen is naturally extremely suitable, so in comparison, Zhu Yunwen is the most suitable candidate.