The Mongol empire ended up being about 127,413,066 square miles, but it did not start out that big. To become such a large empire the Mongols had to gain quite a bit of land and in a short time too, because the Mongol Empire only lasted 162 years. The Mongols accomplished the conquest of a large territory in a short period of time because of tactics (doc,1,2) that allowed them to beat opposing armies. They had a great deal of resources and workforce to supply the armies, (doc 3,4,5,10,11) and with their spread of culture and ideas to regions (doc 6,7) allowed regions to be culturally diverse. With their correspondence with other empires and kingdoms (doc 8,9) they could allow others to know they were a empire to fear. .
While fighting the Cathay people Chingis Khan took the city of fu-chou and Husan -te-fu. He sent an army under the command of Jebe to take the city Chu-yung Kuan. The city was well defended so he tricked their army into thinking that his army was retreating. The Cathayan tribe saw them retreating as they went after them. Jebe army reached the Sondi-i-wu Ridge he turned his army around and beat the Cathayan army, then Chingis Khan commanding the Middle Army attacked to forcing them to retreat. (doc 1) The tricking of the Cathayan Army allowed the Mongols to beat the enemy and conquer another region which added to their empire. The document was an written oral tradition that the Mongols told, which could have been easily changed to the Mongols to appear to be the stronger and scarier. The Tartars were foreigners who took the land of the Ryazan demanded that the Knyazes of Ryazan give them one tenth of everything they had, but the Knyazev refused. They asked for help against the Tartars from Yuri of Volodimir, but he would not help them. Then the Tartar foreigners surrounded the city and took the town on December 21. They killed men, women, children, monks, nun, and priest, even setting them on fire.