Complex sentence: When the Mongols were unified under Khabul Khan in the 12th century, the Jin encouraged the Tatars to destroy them, but the Mongols were able to drive the Jin forces out of their territory.
Split into simpler sentences: When the Mongols were unified under Khabul Khan in the 12th century, the Jin encouraged the Tatars to destroy them. But the Mongols were able to drive the Jin forces out of their territory.