In May 1644, Wu Sangui, a prominent general of the Ming dynasty, faced a critical moment as the Ming rule weakened under pressure from both the Manchus and domestic rebellions. The Ming dynasty had been destabilized by peasant uprisings, most notably the revolt led by Li Zicheng, who had captured Beijing. At this juncture, Wu, stationed at Shanhaiguan, found himself torn between defending the Ming rule and recognizing the shifting tides of power. The Shanhaiguan pass was particularly significant, being the last major barrier protecting the Ming heartland from outside forces.

Wu Sangui decided to open the gates of the Great Wall, a historic gesture signaling his alliance with the invading Manchus. This act not only allowed the Manchus to advance towards Beijing but also facilitated their journey from the northeastern regions of China into the heart of the empire. Wu's motivations were fueled by a desire to maintain stability, save his own forces, and ultimately regain control over the chaotic situation. This alliance, however, would contribute to the swift collapse of the Ming dynasty and the establishment of Qing rule.

The consequences of Wu Sangui's actions were immediate and profound. The Manchus advanced into Beijing after Wu's betrayal, leading to the fall of the Ming court. They eventually declared the establishment of the Qing dynasty, which would rule China for nearly three centuries. Wu Sangui himself later became a key figure in the Qing administration, serving to consolidate their rule. His decision at Shanhaiguan not only changed the fate of the dynasty but also the course of Chinese history, marking a transition to a new era of governance.