After more than a thousand years," he continued, "an enemy finally broke through. Not because of superior firepower. Not because the Manchus were better fighters or strategists. They weren't. The Manchus breached the Great Wall and took Beijing because someone opened a gate. From the inside. As simple as that. A general, a traitor, let them in and an empire fell.
Louise Penny, A Great Reckoning
betrayal, traitor