Why did Genghis Khan conquer the Karakhitai state?

Genghis Khan conquered the Karakhitai state primarily to eliminate a potential threat on his flank and to secure a strategic path for further expansion.

After Genghis Khan defeated the Naiman tribe, their leader's son, Küchlüg, fled to the Karakhitai state, where he overthrew the ruler and seized power. Küchlüg’s subsequent persecution of the majority Islam population in favor of the Buddhist minority created internal instability, which made the state vulnerable to Mongol intervention. The Mongol general Jebe successfully defeated Küchlüg by proclaiming religious freedom and forbidding plunder, effectively winning over the local populace.12

Beyond removing a hostile leader, the conquest served two major strategic purposes:
* Securing the Rear: It prevented other nomadic powers from organizing a military force backed by urban and agricultural resources on the Mongols' flank or rear.12
* Opening New Frontiers: Taking over Karakhitai provided Genghis Khan with a gateway to Khwārezm, offering him an alternative theater of operations to China.12