In the late 1100's a powerful khan named Ghengis Khan (Temujin) came to rule. He organized the Mongol's into a powerful military machine. The Mongol armies were highly mobile and could strike quickly. The main dynasty during the Mongol Empire was the Yuan Dynasty. Kublai Khan then became the emperor during this reign. His goal was to finish the conquest in China that was left off. The Mongols lived apart the Chinese, they were forbidden to marry each other. During his reign the Grand Canal and roads were extended to the capital city. The Yuan Dynasty began to weaken when a series of military defeats occurred.