In 1114, Wanyan Aguda united the Jurchen tribes to rebel against the oppressive Liao Empire. Declaring the establishment of the Jin Dynasty in 1115, he commanded a relatively small but highly disciplined army of fierce Jurchen cavalry. In 1115, as Emperor Tianzuo personally led a massive campaign against the Jin, the Liao royal relative Yelu Zhangnu launched a major rebellion in the rear to depose the emperor. Panicked by this internal coup, the Liao army was ordered to retreat in disarray. Seizing this critical moment, Aguda launched a relentless pursuit, culminating in the Battle of Hubodagang. Here, Aguda's 20,000 cavalry crushed the demoralized Liao host (recorded up to 700,000 in Jin sources, or 150,000 in Khitan records) through lightning-fast shock tactics. The unstoppable Jin cavalry, protected by heavy armor and riding sturdy warhorses, shattered the Liao forces in battle after battle, storming their supreme capital, Shangjing, in 1120. Observing this rapid rise and eager to reclaim the lost Sixteen Prefectures, the Song Dynasty initiated secret maritime negotiations, culminating in the 'Alliance on the Sea' in 1120. They agreed to execute a joint pincer attack to destroy the Liao Empire, with Song striking from the south.
However, the joint campaign exposed the profound military weakness of the Song. General Tong Guan led a massive Song army to attack Liao's southern capital, Yanjing, but was repeatedly routed by a disintegrating Liao garrison. Incapable of taking the city, the Song humiliatingly paid the Jin to capture Yanjing on their behalf. This military embarrassment convinced the Jurchens that the wealthy Song Dynasty was militarily helpless and prime for conquest, laying the strategic groundwork for their future invasion of the Song.
Meanwhile, Jin armies relentlessly captured Liao's main capitals—Shangjing, Zhongjing, and Xijing. The last Liao ruler, Emperor Tianzuo, fled into the western desert, attempting to mount a desperate last stand. In 1125, Wanyan Loushi captured the fleeing emperor, formally ending the 210-year-old Liao Empire. While Prince Yalu Dashi escaped west to establish Qara Khitai (Western Liao), the collapse of Liao made the Jin the undisputed masters of Northern China, now directly bordering the vulnerable Song.
