Mongol siege of Kaifeng

In the Mongol siege of Kaifeng of 1232, the Mongol Empire captured Kaifeng, the capital of the Jurchen Jin Dynasty. The Mongols and Jurchens had been at war for nearly two decades, beginning in 1211 after the Jurchens refused the Mongol offer to submit as a vassal. Ögedei Khan sent two armies to besiege Kaifeng, one led by himself, and the other by his brother Tolui. Command of the forces, once they converged into a single army, was given to Subutai who led the siege. The Mongols arrived at the walls of Kaifeng on April 8, 1232.

The besieged city was deprived of resources, and its residents were beset with famine and disease. Jurchen soldiers defended the city with fire lances and bombs of gunpowder. The Jurchens tried to arrange a peace treaty, but the effort was foiled by the assassination of a Mongol diplomat. Emperor Aizong, the Jurchen emperor, fled the city for the town of Caizhou. The city was placed under the command of General Cui Li, who executed the emperor's loyalists and promptly surrendered to the Mongols. Kaifeng was captured on February 26, 1233, and looted. The dynasty fell two years later after the suicide of Aizong and the capture of Caizhou in 1234.

Background
Genghis Khan was declared Khaghan in 1206. The Mongols had united, under his leadership, and defeated the rival tribes of the steppes. In the same period, China was divided into three separate states. In the north, the Jurchen Jin Dynasty controlled Manchuria and all of China north of the Huai River. The Tangut Western Xia ruled parts of the western China, while the Song Dynasty reigned over the south. Western Xia was subjugated by the Mongols in 1210. In that same year, the Mongols renounced their vassalage to the Jin. Hostilities between the Jin and Mongols had been building up. The Mongols coveted the prosperity of Jurchen territory. They may have also harbored a grudge against the Jin for assassinating Ambaghai, one of Genghis' predecessors, and for the Jin emperor Weishaowang's rude behavior to Genghis when he was still a Jurchen prince.

The Mongols learned that a famine had struck the Jin, and invaded in 1211. Two armies were dispatched by the Mongols into Jurchen territory, with one under the command of Genghis. The Jin built up its armies and reinforced its cities in preparation for the Mongol incursion. The Mongol strategy was based on capturing small settlements and ignoring the fortifications of major cities. They looted the land and retreated in 1212. The Mongols returned the next year and Zhongdu, the capital of the Jin, was besieged in 1213. The Mongols were not able to penetrate the walls of the city in the Battle of Zhongdu, but intimidated the Jin emperor into paying tribute. They withdrew from the city in 1214. Later in the year, fearing another siege, the Jin moved their capital from Zhongdu to Kaifeng. The Mongols besieged Zhongdu once more in 1215 once they learned that the Jin court had fled from the city. The city fell on May 31, and by 1216, huge swaths of Jin territory were under Mongol control.

Meanwhile, the Jin had been inflicted by multiple revolts. In Manchuria, the Khitans, under the leadership of Yelu Liuge, declared their independence from the Jin and allied with the Mongols. Yelu was enthroned a puppet emperor subordinate to the Mongols in 1213. The Jurchen expedition sent against him commanded by Wan Nu was not successful. Wan Nu, realizing the Jin was on the verge of collapse, rebelled and declared himself king of Dazhen in 1215. Further south, rebellions had broken out in Shandong beginning with Yang Anguo's revolt in 1214. The rebels were known as Red Coats, from the color of the uniforms they wore starting in 1215. After the fall of Zhongdu in 1215, the Mongols downsized their war effort against the Jin, and shifted their resources in preparation for the invasion of Central Asia. The Jurchens tried to make up for their territorial losses to the Mongols by invading the Song in 1217. The invasion was fruitless, so the Jin wanted to negotiate for peace, but was rebuffed. By 1218, Jurchen diplomats were prohibited from traveling to the Song. The Mongol war against the Jurchens had subsided, but not stopped, and went on through the early 1220s under the command of the general Muqali. Muqali died from sickness in 1223, and the Mongol campaigns against the Jin wound down. The Jin settled for peace with the Song, but the Song continued to assist the Red Coast insurgency against the Jin. Genghis Khan fell ill and died in 1227. He was succeeded by Ögedei, who renewed the war against the Jin in 1230.

Siege of Kaifeng
Two Mongol armies were dispatched in 1230 to capture the Jin capital of Kaifeng, then named Bian. The plans were to have one army approach the city from the north, while the second attacked from the south. Ögedei Khan headed the army based in Shanxi and his brother Tolui commanded the army stationed in Shaanxi. An illness incapacitated Ögedei and Tolui, and they were forced to step down. Ögedei later regained his health, but Tolui died the next year. Subutai led the combined Mongol forces once the two armies converged in late 1231 and early 1232. The Mongols reached the Yellow River on January 28, 1132, and began amassing around Kaifeng on February 6. The city was besieged on April 8.

The Jurchens tried to end the siege by negotiating a peace treaty. There was some progress towards an agreement in the summer of 1232, but the assassination of the Mongol diplomat Tang Qing and his entourage by the Jurchens made further talks impossible. The Jin were growing desperate. They had enlisted most of the available men in the empire to either defend Kaifeng or fight against the Mongols on the front lines. While the negotiations were ongoing, a plague was devastating the population of the city. Starvation was rampant. The supplies stored in Kaifeng were running out, even with what had been forcibly seized from people. The city's political disintegration created unfounded fears that there was an internal threat. Several residents of the city were executed on the suspicion that they were traitors.

The defense of the city did not collapse immediately. The Jin were able to hold out for months before the city fell. The Jurchen emperor was afforded the opportunity to escape in late 1232, and departed with a retinue of court officials. He left the governance of the city to the General Cui Li and moved to city of Guide in Henan on February 26, 1233, then Caizhou on August 3. The retreat of the emperor was ruinous to the morale of the soldiers defending the city. In the wake of the emperor's departure, Cui ordered the execution of loyalists to the emperor who had remained in the city. He realized that prolonging the siege was suicidal, and offered to surrender to the Mongols. Cui opened the gates of Kaifeng and the Mongols were let into the city. He was later killed outside of battle in a personal dispute, for insulting the wife of someone under his command.

The city was looted when it fell, but atypical to most sieges in the time period, trade was also permitted. The residents of the city sold their luxury belongings to Mongol soldiers for critically needed food supplies. Male members of the royal family residing in the city were captured and executed.

Technology
Herbert Franke observed in his assessment of the battle that the siege is "of some interest for the history of military technology". Many of the details of the siege are known to historians, based on a comprehensive account of the battle compiled by a Jin official living in the besieged city. The Jurchens fired explosives, propelled by trebuchets, at the opposing army. A contemporaneous record of the battle recounts the process by which the bombs were launched. First, a soldier ignited the fuse. The rope of the trebuchet was pulled and the bomb was launched in the air. The bomb produced a large explosion the moment it landed, inflicting damage that could penetrate armor. The explosion sometimes sparked a fire on the combustible grass, which could burn a soldier to death, even if he survives the initial blast. The bombs were more primitive than modern explosives, and occasionally they would fail to detonate or detonated too early. Mongol soldiers counteracted the bombs by digging trenches leading up to the city, which they covered with shielding made of cowhide, to protect from the explosives fired overhead. The Jurchen official reports: "Therefore the Mongol soldiers made cowhide shields to cover their approach trenches and men beneath the walls, and dug as it were niches, each large enough to contain a man, hoping that in this way the troops above would not be able to do anything about it. But someone suggested the technique of lowering the thunder crash bombs on iron chains. When these reached the trenches where the Mongols were making their dugouts, the bombs were set off, with the result that the cowhide and the attacking soldiers were all blown to bits, and not even a trace being left behind."

The infantry of the Jin were armed with fire lances. The fire lance was a spear, attached with a tube of gunpowder. The mixture contained, besides the gunpowder ingredients of sulfur, charcoal, and saltpeter, grounded porcelain and iron filings. The flame that shot from the lance reached a distance of three meters. The heated tinder that ignited the weapon was stored in a small iron box toted by the Jurchen soldiers in battle. Once the gunpowder was consumed, the fire lance could be wielded like a normal spear, or replenished by a new tube filled with gunpowder.

The bombs and fire lances of the Jin were the only two weapons of the Jurchens that the Mongols were wary of facing. The Jurchen deployment of gunpowder was extensive, but it is not certain if the Mongols had acquired gunpowder from the Jurchens before this point in time. Herbert Franke maintains that gunpowder was in the arsenal of both combatants, but Stephen Turnbull believes that only the Jurchens made use of it. The Mongols loaded their catapults with large stones or bombs of gunpowder, which were fired at the Jin fortifications. The barrage inflicted several casualties in the city and had a psychological impact on the soldiers manning the Jurchen trebuchets.

Historical significance
The siege of Kaifeng crippled the Jin Dynasty, but did not destroy it. The penultimate emperor of the dynasty, Emperor Aizong, had evaded capture, but was left destitute after the siege. He sent his diplomats to entreat the neighboring Song Dynasty for help. They warned that the Mongols would invade the Song once the Jin fell, and requested supplies from the Song. The offer was refused. The Song, who had fought multiple wars against the Jin, resented the Jurchens for their conquest of northern China decades earlier. Instead of aiding the Jin, the Song allied with the Mongols. They cooperated militarily and captured the last of the cities still controlled by the Jin. In December 1233, the Mongols besieged Caizhou, where Aizong had fled to from Kaifeng. The emperor was unable to escape the town under siege, and resorted to suicide. On February 9, 1234, the Mongols broke through the defenses of Caizhou. Emperor Modi, Emperor Aizong's intended successor, resided in the same town and was killed in battle soon after. His reign lasted for a total of less than two days, from February 9 to his death in February 10. The Jin Dynasty ended with the fall of Caizhou.