Because the world often regards the Forbidden City as the imperial palace of the Ming and Qing Dynasties, and Li Zicheng withdrew the capital in just one day when he proclaimed himself emperor in Beijing, and the dynasty of Li Zicheng really only existed for one day, and he only became emperor for one day.
Dashun, or Li Shun, was a political power established by Li Zicheng, king of peasant army in the late Ming Dynasty in China history. Dashun first took Xi 'an as its capital, then moved to Beijing, and its territory once included many provinces in the Central Plains. However, it was defeated by the Qing army and finally destroyed by the Nanming regime. 1644 On April 29th, Li Zicheng was enthroned in Wuying Hall of the Forbidden City. Only one day later, he led his team out of Beijing and defeated Xi 'an.
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In fact, from the end of the Eastern Han Dynasty, the so-called "Li Wei Wang" prophecy has been circulating for a long time. Peasant uprisings in past dynasties often used this prophecy to call on the people. In the Ming Dynasty, the "eighteen-child prophecy" appeared formally, and Song Xiance just attached this prophecy to Li Zicheng. Out of professional habit, Song's suggestion meeting is very interested in Liu Bowen's anecdotes, and I'm afraid he won't be unaware of the prediction that "let nature take its course and stop".
Li Zicheng attaches great importance to Song Xiance, "believing in God", and it is necessary to seek Song Xiance's advice to establish the title. Li Zicheng chose the title of "Dashun" probably because he accepted the advice of Song Xiance and others and called himself the terminator of the Ming Dynasty.
References:
Dashun-Baidu encyclopedia