The invasion began in May of 1211. This was no small move on Chingis’s part. The Jin Dynasty, despite the symptoms of dynastic decay which had been reported to Chingis by his various spies, was still one of the five or six great sedentary states of Eurasia. The Jin state had a population of perhaps 40,000,000, although only around 3,000,000 of the populace were Jurchens, descendants of the original Jurchen tribesmen from Manchuria, the rest being Han Chinese and other indigenous peoples. The Jin state could muster 150,000 or so cavalrymen, most of the Jurchens, and 300,000 to 400,000 infantrymen, most of them Chinese. The loyalty of these Chinese infantry was, of course, in question. Still, according to one modern historian, “the Jin army retained a reputation as the most powerful military state in the known world.”
Chingis had under his overall commanded one army of perhaps 50,000 cavalry led by himself, and another army of 50,000 cavalrymen led by three of his sons. His ranks would soon be swollen with discontented tribesmen and deserters from the Jin.
The Mongols first confronted the Onggut, a tribe of nomads which guarded the southern rim of the Mongolian Plateau on behalf of the Jin Dynasty. Their leader Alakush quickly defected to Chingis along with many of his troops, demonstrating just how tenuous a hold the Jurchens had over many of their subject peoples. Loyalists along the Onggut reacted by assassinating Alakush, but at the urging of his nephew and heir the rest of the Ongguts soon fell in line and joined the Chingis’s forces. Several towns near present day Zhangjiakhou (earlier known as Kalgan) on the very edge of the Mongolian Plateau, quickly fell to advancing nomads, and more border troops deserted. Liu Bailin, the Jin commander of the town of Weining defected, and would go on to play a leading role in the defeat the the dynasty.
WIth the Mongols, their ranks now swelled with former Jin auxiliary troops, poised on the very edge of the great ramparts overlooking the farm lands northern China and within a couple days ride of the Central Capital of Zhongdu (Beijing), the Jurchen court panicked and put out peace feelers, apparently thinking that this was just a another Mongol raid in search of quick loot and that Chingis could be bought off with some suitable bribes. When this initial overture was rejected, an senior envoy, a Khitan man by the name of Shimo Mingan who knew the Mongolian language and had earlier met with Chingis in Mongolia, was sent north with more serious peace proposals. Shimo Mingan promptly defected to the Mongols and was made a commander of both Mongol detachments and of native Chinese troops who had now turned on the Jurchens.
The now-augmented Mongolian forces swept down on the North China plain and by the autumn of 2011 they had invested the Jin Western Capital (modern-day Datong, in Shanxi Province). The Jin commander of the Western Capital, a man named Hushahu, who one modern historian describes as an “irascible ruffian,” abandoned his post, allowing the Mongols to take over the city (there were rumors the Mongols had bribed him), and another Jin general, the overall commander of Jin armies in the west, also turned and fled with most of his troops to the Central Capital, even though they far-outnumbered their Mongol opponents. The official history of the Jin Dynasty would later declare that the desertion of their posts by these two commanders was an forboding sign: “The spirit of resolution was lost and could not be regained. The collapse of the Jin was foretold by this event.”
WIth the approaches to the city unguarded, and Mongol armies quickly moved eastward and by the end of the year had invested the main capital of Zhongdu, where the Jin court was headquartered. In early 1212, after laying siege to Zongdu for a month but failing to take the well-fortified city, the Mongols decided to return back to the Mongolian Plateau. Chingis himself had been wounded by an arrow in the battle for the Western Capital and his injury may have contributed to his decision to withdraw. Chingis had by no means been defeated. On their way home the Mongols even detoured eastward to loot the Jin Eastern Capital (current day Liaoyang in Liaoning Province). The Mongols were simply retiring to the fastnesses of the Mongolian Plateau to enjoy their loot, let their horses fatten on the steppe over the summer, and regroup for their next assault. The weaknesses of the Jin Dynasty had been exposed, and Chingis intended to exploit them.
In early 1213 the Mongols again descended onto the plains on North China. The Western Capital was quickly retaken and the main capital of Zhongdu again besieged. While many Jin troops were tied down in the capital, Mongol troops spent the summer and fall rampaging across the North China plain, looting and plundering much of current-day Shanxi, Hebei, and Shandong provinces. By early 1214 the armies had converged on the Central Capital and 1214 Chingis himself was bivouacked in the northern suburbs. The noose again the city was tightened, and his sons, and generals urged him to attack the city and put an end to the Jin Dynasty once and for all.
Inside the city walls the Jin Court was in shambles. Hushahu, the same man who had abandoned the Western Capital in 1211, had made his way to the Central Capital where he made a bid to seize control of the Jin Dynasty himself. First he killed the governor of the city and then seized the sitting Jin Emperor, the hapless Wanyan Yunji, who Chingis had earlier dismissed as an “imbecile.” After ordering court eunuchs to kill Wanyan Yunji he connived to put the aging Wanyan Hun, the older brother of Emperor Zhangzong, who had died back in 1208, on the throne as the new Jin emperor. Hushahu himself hoped to rule as the power behind the throne. But the backstabbing was not over. Shuhu Gaoji, a Jin general who harbored his own ambitions, seized Hushahu and had him executed. Now Wanyan Xun, who Hushahu had intended only as a figurehead, was ruling as Jin emperor. Whether he would be able to right the tottering Jin State and defend it against the Mongols camped outside the walls of his capital was open to question.
Chingis, with his well-developed spy network, must have been well aware of the turmoils in the inner circles of the Jin. Yet when pressed to force the walls of the Central Capital and overthrow the dynasty he hesitated. Plundering the countryside was one thing; actually overthrowing a dynasty and assuming the responsibility for governing its subjects was quite another matter. He had seized control of the Xi Xia Empire to the west while leaving the Tanguts to govern under his suzerainty and perhaps he envisioned the same relationship with the Jin. And there were very immediate, practical considerations to take into account. The siege had already dragged on for months and more months might be required to finally take Zhongdu. The Mongol forces drawn up around the capital were desperately short of food. The Christian missionary Carpini who would later visit the Mongol court claimed that the Mongols outside Zhongdu were so starved that they resorted to cannibalism and had to kill their own comrades for food. One out of every ten died to provide sustenance for the others, he claimed. This may have been a slanderous exaggeration, but numerous other sources attest to the dire straits of the Mongol troops. Rashid al-Din reported that “things were so bad they ate the corpses of their dead companions and of fallen horses; they even ate hay.”
To make matters worse, an epidemic of some unspecified disease soon raged among the Mongol troops, and with the onset of Spring the legendary heat of the north China plain would debilitating to both the nomads used to their cool highlands on the Mongolian Plateau and to their horses. It was not clear how much longer the Mongols could hold out.
Chingis decided to make peace overtures. The Muslim merchant Jafar, a long time camp follower of Chingis who years earlier served as his envoy to the Jin and whose knowledge of the geography of the north China plain had proved invaluable during the invasion, was chosen to negotiate with the Jurchen court. The embattled Jurchens quickly came to terms, offering huge material inducements to persuade Chingis and his men to return to Mongolia. As part of the settlement, according to one source, Chingis received a Jin princess as a wife, 500 boy and girl slaves, 3000 horses, and quantities of gold and expensive fabrics.
The Secret History maintains that Chingis himself got only a princess named Qiguo but that his soldiers received vast qualities of gold, silver, satin, silk, and other expensive goods: “Our soldiers loaded as much of the satin and other goods as they could carry, tied the loads with silk, and left.”
Thus Chingis and his troops returned to the cool steppes of Mongolia returned laden with booty, and there was no doubt great rejoicing among the Mongolian women when they saw the luxurious silks, satins, and brocades their men had brought home for them.