General Knowledge
Why did the Great Wall fail in 1644?
- A general opened the gates
- It was breached
- It had crumbled
The answer is A general opened the gates. The wall was intact - Wu Sangui let the Manchus through at Shanhai Pass.
It did not fail. The Ming dynasty fell because a rebel army took Beijing from the inside, the emperor hanged himself, and the general holding the eastern end of the wall at Shanhai Pass - Wu Sangui - decided he preferred the Manchus to the rebels and opened the gates for them. The Manchus rode through a fortification that was in good order and manned.
That is the honest verdict on the whole structure. Walls of this kind are not barriers so much as tripwires and logistics: they slow raiders carrying loot, carry signal beacons, and let defenders move along the frontier faster than an enemy can move across it. They work when the politics behind them work, and they are irrelevant when the politics fail, which is a pattern that has repeated with every large wall since.
It is also not one wall. Different dynasties built along different lines over some two thousand years, out of whatever was to hand - rammed earth and reeds in the desert west, the familiar stone and brick near Beijing, which is Ming work from the 1500s and the most recent. Long stretches have dissolved back into the landscape, and a government survey in 2012 put the total length of all fragments at over 21,000 kilometres.