Originally, the Mongols were characterized as pastoralists, or herders. They also had what is called a decentralized patrilineal system, which means that they were governed by several people instead of one who gain their position through birth. As pastoralists, they frequently were moving in order to feed their animals and stay with safe climate conditions. They almost always lived near settled people in order to trade the supplies they needed. They were also tough by nature because they had to endure harsh conditions in weather and other.
The Mongols were founded by a guy named Genghis Khan in 1206 (otherwise known as Timogen). According to Britannica, "Before 1206 Genghis Khan was but one of the tribal leaders fighting for supremacy in the steepe regions south and southeast of Lake Baikal; his victories over the Kereit and then the Naiman Turks, however, gave him undisputed authority over the whole of what is now Mongolia (The editors of Encyclopedia Britannica)." In other words, this means that the Mongol government went from many people having control over the land to a single person having control over the land. In this case, that person is the Great Khan. However, in the end military and political counselors associated Khan.
Timogen, who would later be known as the Great Khan, united the Mongol confederation after winning a civil war. He gained favor by promoting people based on their hard work instead of who their family was, and bringing lower class citizens from conquered cities into his tribe while depriving the higher class people of luxuries. This was a common practice among the Mongol empire. After conquering a city, they would absorb the people into their tribe. Because of this, most of the Mongol armies consisted of a high percentage of ethnic groups other than Mongolian.
The success of the Mongol army was not due to strength in numbers, but effective use of strategy and tactics. Their armies fought on horseback in order to maximize speed and mobility while in battle. Signals and other forms of communication were used in order for the soldiers to know exactly what to do. They shied away from hand to hand combat, using only bows and arrows until the enemy lines were in total chaos. They also used spies and propaganda as tactics in battle. Their army was a well oiled and finely tuned machine built for destruction. They were able to take over territories that no one else in history had previously been able to overtake. However, they did have one problem. Their strategies and techniques were best for fighting on flat plains, so they would often need aid from the Chinese, Persians, and/or Arabs when tacking on walled cities. Most times, the Mongols would invade the cities and offer peace in exchange for surrender. If they obliged, the people of use became federates. If they refused, the armies would take over the whole city, killing everyone and / or capturing people to be their slaves. Because of this constant intake of soldiers from different cities, the Mongol army consisted of a very small percentage of ethnic Mongols and a very large percentage of other ethnic groups. In other words, most of the "Mongol army" were not Mongols.
Historically, the Mongols were known to have shown hostility towards people who had been conquered. Those who had been conquered were originally expected to adopt the Mongol social structure. People from these different tribes were treated as objects. In some cases, military leaders would be rewarded with a whole tribe of people or would be given control over all of the people who lived in their area. These soldiers were free to do whatever they wanted with their people. However, later times proved to be very different, as we see that Khan eventually gave the poor people from conquered tribes more luxuries than the richer people from conquered tribes. The Mongols surprisingly were more egalitarian in their beliefs, meaning that they believed everyone to be equal. As crash course states, "When there is less to go around, people tend to share more and when both men and women must work for he social order to survive there tends to be less patriarchal domination of women (Crash Course World History)."
When the black death came into the picture, In the 14th century, the Mongols were accused of being the cause. In one particular story, the Mongols were said to have catapulted their infected men over city walls with the intention of infecting others. However, most likely that is not the case. The plague was likely spread through rats who carried the disease on Mongol trade ships, thereby spreading the disease around. The combination of the black death outbreak and the murder of one of the Golden Horde's caused the horde to begin to decline. By the 15th century, the horde had broken apart into several smaller territories.