However, Goguryeo's population and economy were severely damaged due to the long years of continuous warfare. Yeon Gaesomun died in 666 of a natural cause, and Goguryeo was thrown into chaos and further weakened by a succession struggle among his sons and younger brother, with his eldest son defecting to Tang and his younger brother defecting to Silla. Tang mounted a fresh invasion in 667, aided by Silla and the defector Yeon Namsaeng, and was finally able to conquer Goguryeo in 668.