Mongol Decimal system
Genghis Khan organized the Mongol soldiers into groups based on what is called Mongol decimal system. Units were recursively built from groups of 10 (Arav), 100 (Zuut), 1,000 (Minghan), and 10,000 ([Tumen]), each with a leader reporting to the next higher level.
Tumens, and sometimes Minghans, were commanded by a [Noyan
], who was often given the task to administer specific conquered territories. From two to five Tumens would then form a ''hordu'' meaning army corps or field army, from which the word "Horde" is derived, under the command of the Khans or their generals (''boyan'').
The leaders on each level had significant license to execute their orders in the way they considered best. This command structure proved to be highly flexible and allowed the Mongol army to attack ''en masse'', divide into somewhat smaller groups to encircle and lead enemies into an ambush, or divide into small groups of 10 to mop up a fleeing and broken army.