A major goal of Chinggis was the conquest of Jin, both to avenge earlier defeats and to gain the riches of northern China. He declared war in 1211, and at first the pattern of operations against Jin was the same as it had been against Western Xia. The Mongols were victorious in the field, but they were frustrated in their efforts to take major cities. In his typically logical and determined fashion, Chinggis and his highly developed staff studied the problems of the assault of fortifications. With the help of Chinese engineers, they gradually developed the techniques that eventually would make them the most accomplished and most successful besiegers in the history of warfare.

As a result of a number of overwhelming victories in the field and a few successes in the capture of fortifications deep within China, Chinggis had conquered and had consolidated Jin territory as far south as the Great Wall by 1213. He then advanced with three armies into the heart of Jin territory, between the Great Wall and the Huang He. He defeated the Jin forces, devastated northern China, captured numerous cities, and in 1215 besieged, captured, and sacked the Jin capital of Yanjing (later known as Beijing). The Jin emperor did not surrender, however, but removed his capital to Kaifeng. There his successors finally were defeated, but not until 1234. Meanwhile, Kuchlug, the deposed khan of the Naiman Mongols, had fled west and had conquered the state of Karakitai, the western allies that had decided to side with Chinggis.

By this time, the Mongol army was exhausted by ten years of continuous campaigning against Western Xia and Jin. Therefore, Chinggis sent only two tumen under a brilliant young general, Jebe, against Kuchlug. An internal revolt was incited by Mongol agents; then Jebe overran the country. Kuchlug's forces were defeated west of Kashgar; he was captured and executed, and Karakitai was annexed. By 1218 the Mongol state extended as far west as Lake Balkash and adjoined Khwarizm, a Muslim state that reached to the Caspian Sea in the west and to the Persian Gulf and the Arabian Sea in the south.

Data as of June 1989