If you look at it deeper, the fall of the #Khitan Empire / #Liao Dynasty was when #Goryeo won the #GoryeoKhitanWar#고려거란전쟁#遼麗戰爭. It showed to the world that a smaller country can force the tiger on its knees.
I now understand why the #Kdrama#GoryeoKhitanWar chose the 2nd Goryeo-Khitan War period. (a.k.a. Korea-Liao War)
The "rebellious" General was considered a hero despite his decision to rebel and assassinate his current king.
The prince the General enthroned as Emperor of Goryeo was very successful in repelling the Khitan invasions.
This new Emperor started as a powerless emperor and then became very knowledgeable. In the 3rd Goryeo-Khitan War, he even appointed a politician as a General, and that politician-turned-General brought great victories for Goryeo despite his lack of military experience. (His political experience helped him become a great strategist?)
The emperor did not let anyone to use him as a puppet and truly cared for his people. He rose up and became a great king which brought peace and prosperity during his reign.