General Yi drives his army from the Yalu River straight into the capital, defeats forces loyal to the king (led by General Choe, whom he proceeds to eliminate) and forcibly dethrones King U in a de facto coup d'état but does not ascend to the throne right away.

Instead, he places on the throne King U's son, King Chang, and following a failed restoration of the former monarch, has both of them put to death.

Now the undisputed power behind the throne, General Yi soon forcibly has a Goryeo royal named Yo, now King Gongyang, crowned as king.

After indirectly enforcing his grasp on the royal court through the puppet king, Yi then proceeded to ally himself with Sinjin aristocrats such as Jeong Do-jeon and Jo Jun.