1644
Battle of Shanhai Pass
The setting
Shanhaiguan, where the Great Wall meets the sea, in modern Hebei
The eastern terminus of the Great Wall — a fortified corridor between mountain and sea, roughly fifteen li wide. The one gate through which an army could pass, and it was opened from the inside.
Reveal the outcome
Recorded sideQing (Later Jin) forces with Wu Sangui's Ming garrison
Recorded resultvictory
Qing victory, and the hinge on which the dynasty turned.
How the atlas explains it
It was not won by breaching the wall. Wu Sangui, the Ming general holding the pass, chose the Manchus over the rebel who had just taken Beijing and hanged his emperor, and opened the gate. Dorgon then held his banners back while Wu and Li exhausted each other, and committed the Qing cavalry into a dust storm against a Shun army already fought out. THE DECISION THAT MATTERED WAS MADE BEFORE THE BATTLE AND BY THE MAN GUARDING THE DOOR.
What followed
The Ming had already fallen — Li Zicheng took Beijing in April and the Chongzhen emperor hanged himself. What Shanhai Pass decided was WHO WOULD REPLACE THEM, and the answer was a Manchu dynasty that would rule for 268 years. ⚠ It is also the atlas's clearest case of a battle decided by a defection whose terms were settled in advance, which puts it beside Plassey and Ferozeshah on a mechanism the atlas can now compute rather than assert.