In 1368, after 15 years of armed struggle, the 40-year-old Han hero Zhu Yuanzhang finally crushed Chen Youcheng, Zhang Shicheng, Fang Guozhen, Chen Youding and other southern separatist forces, unified the vast area south of the Yangtze River, proclaimed himself emperor in his base Yingtianfu (present-day Nanjing), established the Daming Empire, and changed the Yuan to Hongwu, which was for the Ming Emperor. In the same year, Zhu Yuanzhang appointed Xu Da and Chang Yuchun, the two most powerful generals in Daming, as the chief and deputy commanders of the Northern Expedition, and sent an army of 250,000 to serve in the Northern Expedition, aiming directly at Dadu (present-day Beijing), the capital of the Mengyuan Dynasty. Under the offensive of the Ming army to destroy the decay, in August of that year, Xu Dabing attacked the capital of Yuan without bloodshed, and the last emperor of the Yuan Dynasty, Emperor Yuanshun, fled to the grassland for Timur, the Yuan Dynasty collapsed, and Zhu Yuanzhang completed the political mission of the Yuan, Ming, and Yi dynasties.
However, the hundred-footed worm died but did not stiffen, Emperor Yuanshun fled to the grassland, still leading the grassland departments in the name of the Great Khan, and the grassland ministries also respected him as a co-master, so that the remnants of the Yuan Dynasty still dominated the north of the Great Wall in the form of the Northern Yuan, as well as Liaodong, and the Goryeo Dynasty on the Korean Peninsula also became a vassal of the Northern Yuan, and the Western Regions were also very close to the Northern Yuan, from the Yalu River to Jiayuguan, the northern border of the Daming Empire that stretched for thousands of miles, always under the threat of the Northern Yuan.
Just as the so-called "Ande warriors guarded the four directions", after Zhu Yuanzhang recovered the north, he immediately arranged for his fierce generals to guard the key places in the north, such as Xu Da sitting in Beiping, Li Wenzhong sitting in Taiyuan, and Feng Sheng and Fu Youde sitting in Shaanxi and Gansu, and at the same time launched many attacks and conquests against the Northern Yuan (Li Wenzhong's Yingchang Dajie, Hongwu's Battle of Lingbei in the fifth year, Fu Youde's seven battles and seven victories on the Hexi corridor, and other battles), further attacking and consuming the strength of the Northern Yuan. However, fighting on the grassland, the Ming army was naturally in a weak position, such as in the Battle of Lingbei, a generation of famous generals, Xu Da was defeated by Wang Baobao, the first general of the Northern Yuan, losing more than 10,000 elite soldiers, Li Wenzhong also almost wiped out the entire army, and the loss of war horses was even more serious. Because of this, after the Battle of Lingbei, the Ming Dynasty and the Northern Yuan entered a confrontation stage, and neither side could break the deadlock for a while.
After that, Zhu Yuanzhang focused his main efforts on the construction of internal affairs, and the Daming Empire gradually came out of the trauma of the late Yuan War. And as time passed, Zhu Yuanzhang's suspicion of meritorious heroes began to become more and more sensitive. But Zhu Yuanzhang is not a fool, he also knows the importance of the army, and understands the truth that the three armies are easy to get and one general is difficult to find, before there is no alternative, Zhu Yuanzhang will not easily raise the butcher knife to the military generals, realistically speaking, the heroes killed by Zhu Yuanzhang in the early stage are mainly some lawless nobles and civil officials, such as Zhu Liangzu, who Hongwu killed in fifteen years, really deserved to die.
In the twenty-fifth year of Hongwu (1392), Zhu Yuanzhang's painstakingly cultivated successor and crown prince Zhu Biao died of illness, and Zhu Yuanzhang immediately appointed Zhu Biao's eldest son Zhu Yunjiang as the crown prince (later Emperor Jianwen), confirming the relationship of heirs. Zhu Yunjiang did not have his father's skill and prestige, in order to ensure that Zhu Yunjiang would not be subject to the meritorious group in the future, Zhu Yuanzhang began a campaign of mass murder of meritorious figures, especially the Blue Jade case, which killed 15,000 people in one case, making the founding name of Daming empty. Lan Yu, Feng Sheng, Fu Youde and other super generals were all killed, and the Daming military was empty.
And most of these famous generals fought against the main force of the Northern Yuan, although the blue jade defeated the Northern Yuan in the Battle of Yuerhai in Hongwu's twenty-first year, the three departments of Tatar, Vara and Woodliangha on the grassland were still strong, and they from time to time went south to harass the northern border defense of Daming. Hearing the war drum Si Liang, Zhu Yuanzhang urgently wanted to solve this problem, otherwise the northern border of the empire would never be peaceful.
To say that Zhu Yuanzhang is a genius, such a tricky problem, he solved it at once, the solution was very rude, that is, let his sons go to the north to fight the border, he sealed 13 clan kings to the border along the Great Wall in one go, it was for the thirteen Sai kings. They were King Han, King Shen, King Liao, King Ning, King Qi, King Yan, King Gu, King Dai, King Jin, King An, King Qin, King Qing, and King Su. Among them, the King of Qin (fief Xi'an), the King of Jin (fief Taiyuan), the King of Yan (fief Beiping), and the King of Ning (fief Daning) were the most powerful, with tens of thousands to hundreds of thousands of troops under their command. Not to mention, these Sai kings really have two strikes to defend the side, they have repeatedly fought together, penetrated deep into the grassland, chased the north, and the grassland was abused.
But Zhu Yuanzhang's arrangement also left a huge hidden danger, that is, these Sai kings all supported the army and self-respect, and Zhu Yuanzhang naturally did not dare to act rashly when he was alive, but Zhu Yuanzhang was not there, who could ensure that these people did not rebel and seize power. In fact, when Zhu Yuanzhang was crowned king, many people in the dynasty foresaw the situation and persuaded Zhu Yuanzhang, but at that time, Zhu Yuanzhang did not want military power to fall into foreign surnames, so he had to take the expedient measure of Sai Wang guarding the border, and as a result, less than a year after Zhu Yuanzhang's death, his fourth son Zhu Di the Prince of Yan rebelled in the fiefdom Beiping (present-day Beijing), and the Daming Empire fell into a 4-year bloody civil war (the Battle of Jingjian), and the seeds of all this were planted by Zhu Yuanzhang when he was on the border.