Genghis Khan, the great ruler of believed in the expansion and consolidation of the Mongols. His motives led to several conquests between 1203 AD and 1227 AD. As a result, many annexed and defeated tribes got incorporated into the Mongolian society. The tribes ranged from willingly submitted Turkic Uighurs to defeated hostile Kereyits. This assimilation affected the existing homogeneous composition of Genghis Khan’s army. The Mongol army was no longer a simple body that could be maintained along the old decimal system division principles. To manage this large heterogeneous body, Genghis Khan created a new division system that revoked all rights of the old ones and divided the army into groups consisting of people from different tribes. Migration from one group to another was restricted. Thus, it can be said that the main reason to fragment the Mongol tribes into new social and military groups was to maintain the huge heterogeneous army and prevent internal conflicts within the groups.