Once Genghis Khan solidified his hold upon Mongolia, he began looking outside its borders. China, with its vast lands and wealth, was an alluring target. One by one, he took on and subjugated the three medieval kingdoms that made up China.
His first major campaign was against the Tanguts, a people who had established a kingdom known as Xi Xia in northwestern China, and had become involved in a tariff dispute with the Mongols. The Mongol army attacked Xi Xia and chased the Tangut forces back to their fortified capital. The Tangut king capitulated. He recognized Genghis Khan as his master, agreed to supply him with troops, and even gave him a princess as a bride to cement their alliance. For Genghis Khan, the conflict was a chance to test out his military, and to see that he needed siege capabilities as well as mobile cavalry [sources: Lane, Lococo].
Next, in 2011, the Mongol emperor took on another foe, the semi-nomadic Jurgen people from Manchuria, who had established the Chin kingdom. In a battle at Huan-erh-tsui, the Mongols' first confrontation with a large foreign army, they outmaneuvered the Jurgens' 70,000-man force and virtually wiped it out.
The Mongols rode back to Mongolia, but they returned in 2013 to raid the Chin kingdom again, capturing vast amounts of silks and gold and taking hundreds of captives, including engineers who helped the Mongols improve their armaments. In addition to copying their rivals' catapults and giant crossbows, they appropriated another Chinese invention — explosives — and put it to fearsome use, in the form of rockets that they fired into enemy ranks to create panic [source: Lane].
Finally, Genghis Khan turned his sights toward the southernmost and largest of the three kingdoms, ruled by the Jin dynasty, one of the most advanced societies in the world. The Jin emperor was so powerful that he assumed the new Mongol ruler would become his vassal — a serious mistake on his part. When his emissaries visited Genghis Khan, the Mongol, insulted, spit on the ground to show his disdain [source: Lococo].
In 1215, Mongol forces attacked and captured Chongdu, one of the largest cities in Asia. The Mongol horsemen rode through the city's streets, firing flaming arrows into the wooden houses, and slaughtering thousands of civilians with their swords. As historian Charles Lane notes, it wasn't just random cruelty. Genghis Khan wanted to send out a message to others who might dare to oppose him [source: Lane].