成吉思汗，为什么被称为草原之王？

Genghis Khan was the leader of the Mongols. 成吉思汗是蒙古人的首领。 He united many tribes on the grassland. 他统一了草原上的很多部落。 His soldiers rode fast horses. 他的士兵骑着快马。 They rode their horses far to the west. 他们骑马一直打到西方。 He built one of the biggest empires ever. 他建起了有史以来最大的帝国之一。 People called him the king of the grassland. 人们称他为草原之王。