To acquire the throne, the Third Prince joined forces with the Nanman people to kill Wan Yulin. When Qiu Yongkang was teaching the craftsmen how to make a killing weapon, he had secretly learned from them.
Now that he had the technology to create a great killing weapon, he secretly made it and gave it to the Nanman people to ambush Wan Yulin's army. If they killed Wan Yulin, he promised them two prosperous cities: Jiang City and Qing City.
Wan Yulin had learned of the Third Prince's plan through the spy he had planted beside him. He had quietly waited for the Third Prince to send the Nanman people a great killing weapon. He had killed the Nanman people and snatched the great killing weapon. He had also arrested the Third Prince, his mother, and her family's supporters on the charge of conspiring with foreign countries.
