1. Corruption in the Ming Dynasty: Since the Jiajing period of the Ming Dynasty, politics has become increasingly corrupt. Since Wanli and the Apocalypse, peasant uprisings have been surging. Seeing that the internal crisis in the Ming Dynasty became more and more serious, the Manchu nobles had long had the ambition to destroy the Ming Dynasty and annex the Central Plains.

2. Lessons from the past: As early as the beacon fire of Li Zicheng rebels spread all over the Central Plains, the Manchu nobles had realized that the peasant rebels had to overthrow the Ming Dynasty before sending troops to enter the customs. At the beginning of the seventeenth year of Chongzhen (the first year of Qing Shunzhi, 1644), Li Zicheng went to Beijing after establishing Dashun regime in Xi 'an.

3. The Wu Department voted for the Qing Dynasty: In the seventeenth year of Chongzhen (the first year of Qing Shunzhi, 1644), when the Ming Dynasty perished in March, Wu Sangui and other Liaodong officials who had retreated into the pass quickly decided to accept the surrender of the Dashun regime. The decision was made first because Wu Sangui and others learned that a large number of Ming civil military commanders had joined Dashun.

Extended data:

In order to enter the Central Plains, the Qing Dynasty recruited soldiers and surrendered to revolt. Huang taiji knew that if Manchu wanted to enter the Central Plains, it must obtain the support of the Han landlord class. Therefore, he attached great importance to the role of Han landlords, intellectuals, Ming officials and generals, and adopted the policy of recruiting and bribing.

In the fifteenth year of Chongzhen in the Ming Dynasty (the seventh year of Chongde in the Qing Dynasty, 1642), the Qing army won an all-round victory in the battle of Jinsong, and the elite of the Ming Dynasty was lost outside the customs, leaving Ningyuan as an isolated city, and the road for the Qing army to enter the customs was completely opened.

Baidu encyclopedia-Qing soldiers enter the customs