The Qing army entered the customs on April 23rd. 1644. During the fierce battle between Wu Sangui and Li Zicheng near Shanhaiguan, the Qing army suddenly came out and dealt a heavy blow to Li Zicheng. On April 29th, Li Zicheng proclaimed himself emperor in Beijing, and on April 30th, Li Zicheng fled Beijing. On the first day of October that year, the emperor shunzhi officially announced in Wuying Hall that "Yanjing was set here to conquer China". By this time, the Ming Dynasty had been extinct for nearly half a year.
Later, after the Qing army entered the customs, it refused to recognize Zhu Yousong's legitimacy as the emperor in Nanjing. On the grounds of pursuing Li Zicheng, he quickly occupied Hebei, Shanxi, Shandong, Shaanxi, Henan, Hubei and other places. After that, all the way south to 1662, the remnants of the Ming Dynasty were completely eliminated.
Extended data
The Qing Dynasty played a certain role in the demise of the Ming Dynasty. At the beginning of the Qing Dynasty, I never thought that one day I could win the whole world. Their goal is to occupy the northeast. After the Ming Dynasty lost the Northeast, it was definitely not enough. Therefore, the Ming Dynasty and the Manchu Dynasty were always in a hostile state.
In order to prevent the Manchu dynasty, the Ming dynasty had to deploy heavy troops at Shanhaiguan. By the day Beijing was breached, Shanhaiguan's troops had not mobilized to defend. But after all, the Ming Dynasty was not directly destroyed by the Qing Dynasty. Therefore, the Qing Dynasty was an accomplice to the demise of the Ming Dynasty. And the direct killer is Li Zicheng.