List 2 causes of the decline of the mongol empire?

One cause was the sheer size of the Mongol empire, due to its size the generals and grandsons of Genghis Khan (the most known Mongol warlord of all time) could not hold it together. 
Another cause was that an empire of this size needed more and more administration which was not being done to the level it needed to be, and this eventually led to the decline as well.