Why did Genghis Khan attack the Jin dynasty in northern China?

Genghis Khan’s decision to attack the Jin dynasty was driven by a combination of long-standing personal grievances, strategic necessity, and the political instability of the Jin state.

• Inherited Feuds: Genghis Khan inherited a deep-seated feud against the Juchen-Jin dynasty, which had historically been a source of conflict for his ancestors and the Mongol people.1
• Strategic Security: To secure his position as the ruler of all Mongols, Genghis Khan sought to eliminate potential rivals on his flanks. By 1209, he secured the allegiance of the Xi Xia state, which removed a potential enemy and cleared the path for an invasion of the Jin.2
• Jin Vulnerability: The Jin dynasty was in a precarious position, having been exhausted by a costly war against the Southern Song dynasty. Furthermore, internal discontent among the non-Juchen populations—specifically the Chinese and Khitan—led many nobles to defect to the Mongol side, providing Genghis Khan with valuable intelligence and local support.2

Following the initial invasion in 1211, the conflict continued for decades, eventually resulting in the total collapse of the Jin dynasty in 1234.34