Internet resources on the Mongol Empire usually dwell on the Mongol conquests of a huge mass of territory. Unfortunately, seldom are the reasons behind the conquests explained. One gets the impression that the Mongols were conquering for the sake of conquering to satisfy their ego of becoming the biggest land conquerors in world history on the Guiness Book of Records. However, this is seldom so because of the huge costs of war.
Given the relatively small population of the Mongols (less than 3m today), even Mongolia itself should be enough. Surely, after conquering significant parts of China, it should be more than enough. Why did the Mongols still want to move on to conquer the other parts of Asia, Russia, Europe? What purpose do these territories serve them? Even if they manage to conquer successfully, it is doubtful if the Mongol population was large enough to spread throughout the conquered territories to rule and preserve their power on a long-term basis.
What reasons drove the Mongols to want to conquer such a huge land territory?