In the summer of 1227, Genghis Khan died of illness during his western campaign against the Western Xia. Before his death, he lay on his sickbed and instructed his generals on the best strategy to destroy the Jin Dynasty, which was to join forces with the Southern Song army to attack the Jin together.
After Genghis Khan's death, the position of Great Khan of the Mongols remained vacant until two years later, when the Mongol tribes held a Kurultai assembly on the banks of the Kerulen River and elected Genghis Khan's third son, Ögedei, to succeed him as Khan; after Kublai Khan established the Yuan Dynasty, he posthumously honored Ögedei as Emperor Taizong of Yuan.
Ögedei spent his life campaigning across the north and south. In his early years, he followed his father, Genghis Khan, to conquer the various tribes north of the Gobi Desert and earned considerable military merit in the campaigns against the Western Xia and Jin dynasties. When Ögedei ascended the throne, he was already over forty years old. He reigned for a total of twelve years, during which he carried on Genghis Khan's legacy by continuing to attack the Jin, Western Xia, and Southern Song dynasties, successfully conquering northern China and vast territories in Central Asia. Among his achievements, the destruction of the Jin Dynasty stands as his greatest military feat.
Ögedei's conquest of the Jin Dynasty can be roughly divided into three stages: the first stage, from autumn 1230 to spring 1231, targeted Fengxiang, Tong Pass, and Weizhou; the second stage, from autumn 1231 to spring 1232, saw the Mongol army advance deep into Jin territory, concentrating forces to attack the Jin eastern capital; the third stage, from summer 1232 to spring 1234, followed Genghis Khan's strategy for destroying the Jin, with the Mongols allying with the Southern Song to attack the Jin, ultimately leading to its downfall.
In the first phase, the Mongol army divided into three routes to attack Fengxiang, Tong Pass, and Weizhou respectively. In April 1231, Ögedei's brother Tolui led the western route army to capture Fengxiang. Ögedei personally commanded the central route army, advancing triumphantly through Tongzhou, Huazhou, Jingzhao, and Tong Pass, achieving notable military successes. The eastern route army focused on besieging the Jin dynasty's key military stronghold of Weizhou, and before long, the Jin forces were defeated and retreated, allowing the Mongols to successfully occupy Weizhou.
In the second phase, the Mongol army once again divided into three routes: the left route, led by the great Mongol general Ochen Noyan, attacked Jinan in Shandong; the right route, under the command of Tolui, passed through Southern Song territory to strike at the Jin forces stationed along the Han River at Tang and Deng; the central route, personally commanded by Ögedei, crossed south over the Yellow River and launched a major assault on the Jin eastern capital.
Upon hearing that the Eastern Capital was under siege, the Jin troops stationed in Dengzhou rushed to provide reinforcements, only to be ambushed and intercepted by Mongol forces along the way, suffering heavy losses. Several Jin generals were killed by the Mongol army, and the remaining Jin troops, lacking leadership, fell into chaos. After fleeing to Junzhou, they were once again surrounded by the Mongol forces. Following this series of battles, few Jin generals were left, and the main Jin army had been virtually annihilated.
In early 1232, the Mongol army began besieging the Jin Dynasty's capital, Dongjing (present-day Kaifeng). The reigning Emperor Aizong of Jin was extremely incompetent and cowardly; seeing the Mongol forces pressing in, he actually abandoned the soldiers and civilians of Dongjing and hastily fled to Caizhou to seek refuge. The Jin generals and people were deeply disappointed, morale plummeted, and Dongjing quickly fell to the Mongols. Soon after, the Jin central capital, Zhongjing (present-day Luoyang), was also captured by the Mongol army, and the fall of the Jin Dynasty was imminent.
In the third phase, the Mongols sent envoys to negotiate with the rulers of the Southern Song Dynasty, and the two sides eventually reached an agreement to join forces and destroy the Jin Kingdom together. In the autumn of 1233, the Southern Song dispatched an army of twenty thousand troops, led by the great general Meng Gong, marching northward, while the Mongols sent their general Tachar to lead his forces on the campaign. The Song and Mongol armies converged outside the city of Caizhou, the capital of the Jin Kingdom.
One month later, tens of thousands of Jin troops attempted a breakout from the east gate of Caizhou City. Meng Gong led his forces to confront them, capturing a large number of Jin soldiers. According to the prisoners, due to the prolonged siege, food shortages had already emerged within Caizhou. After consulting with Tacha'er, Meng Gong believed that by continuing to tighten the encirclement—preventing both the city's defenders from breaking out and any outside Jin reinforcements from providing support—Caizhou would soon run out of supplies and fall without the need for a direct assault.
Over the next three months, the Mongol and Song armies besieged Caizhou City so tightly that it was like an impenetrable iron barrel, with no one able to enter or leave. During this time, all the food inside the city was completely consumed, and the Jin soldiers and civilians, driven by hunger to eat anything, descended into cannibalism—a scene of sheer horror.
Tachaer and Meng Gong seized the opportune moment and launched a full-scale assault on Caizhou City in the first month of 1234. Emperor Aizong of the Jin Dynasty, seeing that the Jin state was inevitably doomed to destruction and unwilling to become a ruler of a fallen kingdom, hastily passed the throne to the Jin general Wanyan Chenglin, who is historically known as the Last Emperor of the Jin.
Tachaer led his troops to attack the west gate of Caizhou City, while Meng Gong led his forces to assault the south gate, ultimately breaching the city. Emperor Aizong of Jin committed suicide, and the newly enthroned Emperor Modi of Jin also perished amidst the chaos of battle. Emperor Modi of Jin holds the distinction of being the shortest-reigning emperor in Chinese history, having died less than a day after ascending the throne. Thus, after 119 years since its founding, the Jin Dynasty came to an end. With this, Ögedei finally fulfilled his father's dying wish to destroy the Jin.
During the joint Song-Mongol campaign against the Jin Dynasty, Emperor Aizong of Jin sent an envoy to the Southern Song to negotiate with the reigning Emperor Lizong of Song. The envoy conveyed Emperor Aizong's message: once the Jin Dynasty fell, the Mongols' next target would inevitably be the Southern Song. If the Southern Song abandoned its alliance with the Mongols and instead cooperated with the Jin, both the Song and Jin states could be preserved. Why not take this advantageous course?
However, because the Mongols had previously promised the Southern Song during their alliance that once the Jin state was destroyed, territories like Henan would be returned to Southern Song governance, Emperor Lizong did not take the Jin envoy's words to heart.
Emperor Lizong, having focused all his hopes on recovering lost territory after the destruction of the Jin Dynasty, never expected that Ögedei would go back on his word and refuse to return Henan to the Southern Song. In the end, just as Emperor Aizong of Jin had predicted, the Southern Song was destroyed by the Mongols.