How did the mongols create their huge empire and what areas were included in it?

(My opinion, no one cared, nothing big was happening at the time, the biggest thing at the time in the world during the "rise of the mongol empire" was France outlawing dice games) But okay the reason why the Mongol Empire grew to its largest was that they unified all the tribes and had a specialty of riding horseback with archery. Their Horsemen were unparalled at this time.