[Why] After Li Zicheng broke Beijing, the Shanhaiguan defender Wu Sangui faced the threat of the peasant army. Meanwhile the Manchu Eight Banners outside the pass had long been gathering momentum, seeking the ultimate geopolitical opportunity to enter and master the Central Plains. [What] Wu Sangui in towering rage opened the pass and surrendered to the Eight Banners. Dorgon led the elite Manchu-Mongol Eight Banners main force in long-distance driving through Shanhaiguan, crushed Li Zicheng's main force, and then swung north to capture Beijing and establish unified rule. [Who] Prince Regent Dorgon was the Eight Banners political-military supreme designer of unmatched grand strategy and decisive grasp of historic opportunity. Wu Sangui was a renowned general who changed the historic process of Ming-Qing transition by opening the city and welcoming the enemy. [How] The Qing army entering the pass laid the historic starting point of Great Qing Empire's unified rule over the entire country, definitively reorganizing the territorial map of the Northeast, Mongolia, Xinjiang, and Tibet. It became the final foundation-laying of the multi-ethnic empire.
Why
The historic event of Qing Army Enters the Pass represents a key developmental peak of the Huaxia dynastic system. The final great dynastic expansion across ethnic frontiers. By establishing this moral or administrative benchmark, it continues to shape the structural and philosophical fabric of ancient Chinese statecraft.