In 1206, Temüjin successfully unified the highly fragmented and warring steppe factions, ascending the throne as Genghis Khan at the Onon River and proclaiming the Mongol Empire. Seeking to avenge generations of humiliation and eliminate northern threats, Genghis Khan set his sights on conquering the neighboring sedentary empires, prioritizing military reforms to turn his nomadic warriors into a highly disciplined, swift cavalry force.
Before launching a direct assault on the powerful Jin Dynasty, Genghis Khan initiated the conquest of Western Xia (1205–1210) to secure his empire's southern flank. The Mongol forces marched against the Tangut capital of Xingqing. Utilizing ruthless siege tactics, they went as far as redirecting the waters of the Yellow River to flood the city, forcing the Western Xia court to submit. With Western Xia successfully subjugated as a vassal state, the Mongol Empire secured its rear and prepared for the grand invasion of Northern China.
The massive war against the Jin Dynasty erupted in 1211. Although the Jurchen Jin was a massive empire with tens of millions of people and heavily fortified walls, it suffered from deep internal divisions and political instability. Capitalizing on these vulnerabilities, Genghis Khan bypassed the heavily defended mountain passes of the Great Wall, launching a surprise attack deep into the Jin territory. In 1211, the Mongols achieved a monumental victory at the Battle of Yehuling, decimating the Jin's main field armies using superior cavalry mobility and coordination.
Following their tactical triumphs, the Mongol forces relentlessly pushed deeper into the Jin heartland. In 1215, after a prolonged and devastating siege, Genghis Khan's forces captured the Jin imperial capital of Zhongdu (modern-day Beijing). Plundered and devastated, the loss of Zhongdu dealt a fatal blow to the Jin Dynasty. To evade complete destruction, the Jin Emperor hastily relocated the imperial capital southward to Kaifeng, leaving Northern China under Mongol control and barely surviving in a severely weakened state.
