The Mongol military tactics and organization enabled the Mongol Empire to conquer nearly all of continental Asia, the Middle East and parts of eastern Europe.
The original foundation of that system was an extension of the nomadic lifestyle of the Mongols. Other elements were invented by Genghis Khan, his generals, and his successors. Technologies useful to attack fortifications were adapted from other cultures, and foreign technical experts integrated into the command structures. In many cases, they won against significantly larger opposing armies.
Transfers between units were forbidden. 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. Individual soldiers were responsible for their equipment, weapons, and up to five mounts, although they fought as part of a unit. Their families and herds would accompany them on foreign expeditions.
Above all units, there existed an elite force called Kheshig. They functioned as imperial guard of the Mongol Empire as well as a training ground for potential young officers, the great Subutai having started his career there.
Each Mongol soldier typically maintained 3 or 4 horses. Changing horses often allowed them to travel at high speed for days without stopping or wearing out the animals. Their ability to live off the land, and in extreme situations off their animals (mare's milk especially), made their armies far less dependent on the traditional logistical apparatus of agrarian armies. In some cases, as during the invasion of Hungary in early 1241, they covered up to 100 miles (160 km) per day, which was unheard of by other armies of the time.
The mobility of individual soldiers made it possible to send them on successful scouting missions, gathering intelligence about routes and searching for terrain suited to the preferred combat tactics of the Mongols.
During the invasion of Kievan Rus, the Mongols used frozen rivers as highways, and winter, the time of year usually off-limits for any major activity due to the intense cold, became the Mongols' preferred time to strike.
To avoid the deadly hail of missiles, enemies would frequently spread out, or seek cover, breaking up their formations and making them more vulnerable to the lancers' charges. Likewise, when they packed themselves together, into dense square or phalanx style formations, they would become more vulnerable to the arrows.