This thesis studies the development of Mongolia from disunited tribal communities to the Mongol Empire with special reference to the army and the two great khans. The central focus are the two greatest khans who were most responsible for the rise of the Mongol Empire: Genghis Khan and Kublai Khan. The state of Mongolia before the rise and the achievements and changes that took place during its reign are studied. A comparison of the state of the army during both khans and the influence of the appearance of gunpowder was also made. The goal of the thesis is to see and compare how Mongolia, as a country inhabited by numerous disunited tribes, became one of the longest-lasting and largest empires in history, which lasted until the 16th century. Each Khan had his own way of ruling and vision of what Mongolia should look like. Genghis was a ruler who managed to unite the tribes with his charisma and skill in warfare, and for him the government should remain centralized and traditional, while the army had to be composed of capable and disciplined people. Kublai Khan turned Mongolia into a trade center that connects the Far East with the West, and unlike Genghis, he believed that he should rule according to the model of China and its teachings. He also believed that he was prosperity in progress and changed the style of warfare of the Mongols. It is important to note that Genghis and Kublai belong to the same family and that although they had different views on how it should be ruled during their rule, Mongolia was the strongest during their rule.