What made the Mongols cruel?
The mongols were a nomadic war tribe, they often used raiding war parties to conquer and overcome rivals.
Because the Mongols were a nomadic people, they facilitated cultural diffusion in China, a traditionally isolated society. Also, the Yuan Dynasty in China was made up of Mongols, and ruled for a long time. The Mongols took over the government, but they left many Chinese people in positions of authority and left the civil service exams intact; however, resentment of Mongol rule increased the distrust of foreigners in China.
While China was under rule by the Mongols during the Yuan Dyansty, merchants social status were higher and travelers were free to come and go in Asia. Because of this many people spread word of the wealth in China thus, prompting more people to travel to China. The Mongols also made it safe to travel along the Silk Road.