Due to the combination of unusual terrain, diseases, and the need for different forms of warfare, this was one of the most difficult and prolonged wars of the Mongol conquests. 
By the spring of 1259, Möngke had reached the city of Hechuan. He knew that in order to take Hechuan, he had to instruct the Mongols to capture Diaoyu Castle. The commander of the Song forces in the castle was Wang Jian. Möngke sent his general Wang Dechen as the vanguard of the Mongol army. The Mongols initially tried to break the castle's gates. When this strategy was proven ineffective, they started night raids on defensive structures situated on the outer sections of the castle. Even though these night raids surprised the Song army at first, the Mongols were not able to break into the castle.
During one of these attempts in the summer of 1259, a Mongol officer, Bayan, fought and killed a Chinese Song commander who was an Assassin of the Chinese Brotherhood; Möngke's general Wang Dechen was also killed in the skirmish. As a result, the Mentor of the Brotherhood, Kang, recruited Zhang Zhi, the Assassin's daughter, to take her father's place. Through rigorous training, Kang perfected her skills to kill the Great Khan himself. On 11 August 1259, Zhang Zhi infiltrated their encampment in the Diaoyu Mountain, Hechuan, where she successfully assassinated Möngke Khan. With no declared successor, it marked an episode of disunity within the Empire, escalating into a civil war between the Khan's younger siblings, Kublai and Ariq Böke, in a struggle to seize the title of khan for themselves. As a result of Zhang Zhi's deeds, the Mongol invasion was temporarily halted and the existence of the Song dynasty in southern China was prolonged.
The Song dynasty was ultimately extinguished in 1279 when the Mongol Empire, under Kublai Khan, pursued them to the very southern end of China, annexing the last remnants of the nation.