In the seventeenth year of Chongzhen in the late Ming Dynasty, there was a great war between Li Zicheng, Wu Sangui and Dourgen in a stone near Shanhaiguan, which affected the historical trend. In the first world war, Li Zicheng suffered a crushing defeat, and Beijing, which had just occupied for a few days, fell and did not recover until its demise. Assuming that Wu Sangui did not join hands with the Qing court, but turned Dourgen away, could Li Zicheng still rule the country according to his wishes?
First, Li Zicheng will encounter the same problems as Chongzhen, fighting on both sides. He was even worse than Chongzhen, because Li Zicheng had only five and a half provinces of Hebei, Shandong, Shanxi, Shaanxi and Henan, and half of Huguang, of which Shandong and Hebei just occupied new territory a few days ago. Daming is two cities and thirteen provinces, and he is less than half. Financial resources, resources and manpower can't be compared, what's more, the area he occupies is a poor north created by years of war. These places alone cannot compete with the Qing court and the south for a long time.
Second, Li Zicheng's behavior before and after he entered Beijing was still bandit, killing the royal gentry and using stolen property to keep the army and the local government running. Without production, there would be no continuous financial support, and the most important thing is to push all the gentry to the opposite side. In history, when the Qing army went south, a large number of gentry in the south of the Yangtze River surrendered to the Qing court, but I'm afraid it's not so easy for Li Zicheng to conquer the south, and the gentry are expected to fight to the death.
Thirdly, Li Zicheng has no long-term planning, which is related to his lack of support from scholars. Historically, Li Zicheng put forward political slogans to win people's hearts only after Yan Li, Liu Jinxing and others took refuge.
Until I went to Beijing, there were only a few juren around me, and I didn't have a correct concept of how to govern the country, and I didn't even know anything about the Qing court outside the Great Wall. Maybe he will gradually learn to understand after he proclaimed himself emperor, but the Qing army will enter the customs at any time. He just faced the powerful Qing army and had no time to learn from him. The northern people were looted by the Qing army in Chongzhen Dynasty. If it was robbed in Dashun Dynasty, what do people think of the new Dashun Dynasty?
Fourthly, Li Zicheng's coming from behind is inseparable from the important role of political slogans. The slogan of "welcome the king without food" is deeply rooted in the hearts of the people. This is also the reason why Li Zicheng can only rob money from the pockets of former officials of the Ming Dynasty after he entered Beijing, but can't levy taxes immediately. If he doesn't accept food, he can't keep the huge army and the new court running, but if he accepts food, his reputation will be lost, which is difficult to deal with.
To sum up, even if Wu Sangui helped Li Zicheng guard Shanhaiguan, the Qing army could not have been in the Central Plains for a long time, but the entry war of Chongzhen Dynasty came so many times, coupled with the hostility of the south, Li Zicheng was probably crazy, had no money, and had no support from the upper gentry. Whether the Dashun dynasty can gain a foothold is a big problem, not to mention that both the north and the south are enemies.
The best result is that Li Zicheng gives up Shandong and Hebei, returns to Shaanxi to manage well, holds Shanxi and becomes a bully. This is what he asked Emperor Chongzhen when he was killed in Beijing. Li Zicheng has no motive or mind to unify the whole country. The worst result is that history is still history. He withdrew from Hebei, but the Qing army came in, gradually killing him and the south and continuing to unify the country.