How did the Mongol Empire become such a powerful force in Central Asia and Eastern Europe?

Mongol expansion into Central Asia began in 1209, as the Mongols pursued tribal leaders who opposed Chinggis Khan's rise to power in Mongolia and thus constituted a threat to his authority there. With their victories, the Mongols gained new territory. Indeed, the Mongols cultivated this idea. The Mongol invasion of Central Asia however would entail the utter destruction of the Khwarezmid Empire along with the massacre of much of the civilian population of the region. During the invasion of Transoxania in 1219, along with the main Mongol force, Genghis Khan used a Chinese specialist catapult unit in battle. Hope this helps!