A general invited rivals through the Great Wall, then a sandstorm decided who ruled China

Late on the day of battle, sand filled the air near Shanhaiguan, the fortress where the Great Wall meets the sea. Men swung swords and spears and fired crude cannon, then could barely see. When the rebels rubbed the grit from their eyes, a fresh army was riding at them, its soldiers with the fronts of their heads shaved and their hair braided long behind.

Those horsemen were the Qing, the Manchu led force from beyond the Wall. Their commanders had held their troops back from the early fighting, and they unleashed them when the storm hit.

The battle was the climax of a collapse. Rebel leader Li Zicheng had taken Beijing and ended Ming control of the capital, then proclaimed his own short lived Shun dynasty. Up on the frontier, Wu Sangui, the last strong general of the Ming and the man assigned to keep the Manchus out, faced an impossible choice. The capital needed him, but according to some accounts the rebels were holding his father and possibly his girlfriend hostage.

Tradition holds that Wu chose to ask his enemies for help. He went across the frontier to the Qing and asked the seven year old Qing emperor, Shunzhi, to help save Beijing from the rebels. The boy emperor's uncles, Dorgon, Jirgalang, and Dodo, commanded the Qing armies in the field. They had waited years for an invitation to march through the pass Wu had guarded, and they accepted.

So Wu's Chinese troops and Li's rebels marched east to meet at Shanhaiguan in 1644. At first, the fighting was largely Chinese against Chinese, Wu's men against Li's. Dorgon and Dodo held their Qing troops back a little and let the two sides wear each other out.

Then, according to legend, a sandstorm enveloped the field, blinding the combatants. Anyone who knows North China would find that plausible. Exhausted and blinded, Li's men were suddenly hit by the full Qing force. It was not Manchus alone, but Mongol cavalry, Manchu bowmen, and Han Chinese foot soldiers who had already changed sides.

Li's army broke and the road to Beijing lay open. On the city walls, residents saw Wu's standard approaching and thought they were saved. Then they noticed something else. Wu himself had adopted the Qing hairstyle, shaved in front. Dorgon rode in beside him on what amounted to a peacekeeping mission to restore order, and the peacekeepers stayed, ruling China from Beijing until 1912.