The Mongols Had a Well Organized Military Structure
Genghis Khan organized the Mongols for war. He was a good judge of men, a great talent spotter, and his system was a meritocracy where the capable could rise, regardless of origins. He subjected the formerly fractious and feuding nomadic warriors to strict military discipline that was hard, but not overly harsh or unreasonable. And he drilled and trained them constantly.
He then placed them in a well organized hierarchical organization, with a clear cut and effective chain of command. He created a military organization based on decimals, with a hierarchy of ranks. At the base were squads of 10 men, known as an Arbans. 10 Arbans formed a company of 100, known as a Zuun. 10 Zuuns were combined into a regiment of 1000, known as a Minghan. 10 Minghans were formed into a division of 10,000, known as a Tuman. A separate imperial guard of 10,000 men protected the Khan and leading Mongol figures.
All Mongols had been riding horses since they were toddlers, and were taught archery since early childhood. As a result, they were prime cavalry material by the time they joined the Mongol army as young men. In the army, they underwent extensive and continuous training that transformed them into a mounted elite. They practiced the individual skills of archery and horsemanship almost daily. They also trained constantly to master unit tactics. They drilled in maneuvers, formation changes, rotations, advances, retreats, and massed archery, until they became second nature.
Six out of every ten Mongols were light cavalry horse archers, while the remaining four were heavy cavalry, typically armored and armed with lances. A favorite battlefield tactic, for which they incessantly trained, was to attrit their opponents from a distance with arrows. Once the Mongol commander judged the enemy sufficiently weakened, a signal would be given for a charge, spearheaded by the heavy cavalry, in which Mongol horsemen slashed the survivors with sabers, or skewered them with lances. Another tactic they practiced constantly was a feigned retreat to lure the enemy into pursuing them. Then, once brought to favorable ground, the Mongols would turn at a signal, and surround or counterchange their pursuers.
In short, Genghis Khan transformed the Steppe nomads from warrior bands into a disciplined professional army, with an established structure and hierarchical chain of command. He built on the inherent strengths of the nomads – hardihood, excellent horsemanship, and martial skills such as archery. When those strengths were coupled with discipline and professionalism, the result was a formidable fighting machine.