In 1629, Li Zicheng led more than a hundred people to participate in the peasant revolt at the end of the Ming Dynasty. The Ming Dynasty and Li Zicheng fought a long battle, and after more than a decade of fighting, Li Zicheng, instead of suppressing it, became stronger and stronger, and finally occupied Beijing in 1644 and overthrew the rule of the Ming Dynasty. However, instead of being able to unify the whole country, Li Zicheng fought against the Qing Dynasty for only one year and was completely defeated.
There are many reasons for Li Zicheng's failure, both political and economic, but we will not discuss these today, but only analyze this problem from a military point of view! When Li Zicheng occupied Beijing, he could be said to have unified the northern regions of the Ming Dynasty, and Gansu, Ningxia, and Shaanxi in the northwest, as well as all of Shanxi, Hebei, Henan, and Shandong in the north, as well as the northern part of Hubei, were under the control of Li Zicheng's Dashun army, and his army was at least 500,000 or more.
First, pride is light on the enemy, and it is not expected that the Qing Dynasty will participate in the war. In April 1644, Li Zicheng personally led a large army to Shanhaiguan to prepare for a decisive battle with Wu Sangui, but he only sent the Ming general Tang Tong to lead thousands of troops to defend a stone area, and was not prepared to defend the Qing army, and as a result, this force was quickly destroyed by the Qing army. After the Battle of Shanhaiguan began, Li Zicheng threw in all his troops to attack Wu Sangui's troops, leaving no "reserves".
The two sides fought from morning to noon, and Li Zicheng's army gradually gained the upper hand. At this critical moment, tens of thousands of elite cavalry of the Qing Dynasty suddenly came out from the flanks, and the peasant army was suddenly overwhelmed, and the general Liu Zongmin was wounded. Li Zicheng saw that the defeat had been decided, so he had to lead his army to retreat. However, the Qing Dynasty cavalry pursued it relentlessly and chased for more than forty miles, and the peasant army, which was mainly infantry, was defeated and could not be defeated, and the losses were very heavy.
Second, in the field war with the Qing army, there was a lack of firearms and artillery. In the early years of the Qing Dynasty, the combat effectiveness of the Eight Banners Cavalry was very strong, especially in field battles, which were difficult to defeat. Therefore, after the Battle of Ningyuan, the Ming Dynasty basically adopted Yuan Chonghuan's strategy of "building a strong city and using cannons" to deal with the Eight Banners cavalry of the Qing Dynasty. However, before the Battle of Shanhaiguan, Li Zicheng did not know much about the Qing Dynasty, so he still used tactics against the Ming Dynasty to deal with the Eight Banners cavalry.
In the course of the battle between the Dashun army and the Qing army, Li Zicheng almost always set up a position in the plain area and fought a field battle with the Qing army head-on. After withdrawing from Beijing, the Dashun army launched a series of battles with the pursuing Qing army, such as the Battle of Dingzhou, the Battle of Zhending, and the Battle of Tongguan, all of which used the frontal field method, and all of them were defeated. In the midst of Tongguan, the Dashun army also exposed another problem, they lacked artillery, and the Qing army used artillery to open the gate of Tongguan.
Third, mobile operations, there is no rear strategic base. In the first month of 1645, Li Zicheng left Xi'an, where he had established the Dashun regime a year earlier, personally leading his troops north, and this time he was forced to leave. Although Li Zicheng occupied most of the northern region, he did not carry out local construction in time, resulting in these areas being quickly lost with his military defeat. In March of the same year, Li Zicheng arrived in the Xiangyang area of Hubei Province, where he also controlled four provinces and had an army of 200,000 in his hands.
However, Li Zicheng did not stay here, taking this as the meaning of the base area, but wanted to go down the river, "claiming to want to take Nanjing, advancing by land and water." Zuo Liangyu could not defeat Li Zicheng, abandoned Wuchang, and took a boat to the east. However, Li Zicheng's life was not good, he led hundreds of thousands of people, neither to provide food and pay from the rear, but also to protect his family, so he was soon caught up by the Qing army. After several engagements, the Dashun army suffered heavy losses. In May, Li Zicheng entered the Jiugong Mountain area and was inadvertently killed by the local regiment.
References: 1. Peasants' War at the End of the Ming Dynasty; 2. History of the Ming Dynasty