Mongol conquest of China

The Mongol Conquest of the Song Dynasty was an invasion of the Song states in southern China by the Mongol Empire led by Möngke Khan and later Kublai--both grandsons of Genghis Khan.

The resistance of the Song army in Sichuan was ineffective. By the spring of 1259, Möngke reached the city of Hechuan. In order to take Hechuan, the Mongols had to capture the 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 the outer part of the castle on minor defensive structures. Although these raids surprised the Song army at first, the Mongols were not able to break into the castle.  

During one of these attempts, a mongol officer, Bayan, fought and killed an unamed Assassin of the Chinese Brotherhood. As a result, Zhang Zhi, the Assassin's daughter, swore revenge on the Great Khan and trained rigorously to become a highly skilled Assassin. On August 11, 1259, Zhang Zhi infiltrated their encampment in the Diaoyu Mountain, Hechuan where she found and successfully assassinated Möngke Khan, plunging the Empire into division and straight into civil war between the Khan's younger siblings, Kublai and Ariq Böke, in a struggle to seize the title of Khan for themselves. The invasion was temporarily halted from destroying the Song Dynasty.