The sudden change in Li Zongming's attitude was because Zhang Lie hadn't taken his life even when he was clearly capable of doing so. However, Li Zongming was the king of the realm, and he certainly couldn't let Zhang Lie go so easily. 

Zhang Lie had ruined the wedding between east and west, crippled the king of the west's son, and kidnapped his own daughter. He had destroyed the two kings' reputation, and Li Zongming could hardly be seen to side with him or to give him any quarter.

In order to maintain the dignity of his position as the king of the realm, Li Zongming had to strike with full force. If Zhang Lie were able to survive...