For which reasons were the Mongols so successful?
Mongols were successful for a number of central reasons. The first of these reasons was their sheer size, with some accounts describing their numbers at being over one million at the peak of their strength. Another reason for their success was due to the organization of the army, which was largely cavalry based and needed no supply train.
This meant that their army could travel far quicker and with far less supplies than conventional armies, meaning they could travel twice as far as other armies in some cases. The Mongolian people are traditionally nomadic, and so they had no issues with being on the march for months if not years at a time and could easily live off the land. A third reason behind their success was their military tactics, which saw most soldiers using bows and arrows to engage the enemy and then retreat before they could be engaged by the enemy. This led to widespread confusion within the enemy ranks and made it easy for the Mongol soldiers to pick off fleeing enemy troops.
Another reason for their success was their choice of authority. The Mongols ruled with a double edged sword of clemency and violence. If a kingdom or leader refused to surrender to them, then they would destroy every facet of their kingdom and often destroyed entire cities in retaliation of rebellions. If a leader chose to surrender, however, they would be shown a relative amount of peace and would only be forced to pay an annual tax to their Mongol leaders.
These societies would be free to then practice their own religion, way of life, and legislation with no interference from the Mongolian leaders. In all, the Mongols managed to conquer such an enormous area of the world due to their sheer size, organization, military tactics, and ruthlessness.