So yeah, your challenge is to have the Kwarezemians defeat Mongol expansion at their borders. They can be pushed back but they need to definitively stop mongol expansion in that direction.
EDIT: Oh and because I always tell other people to do this but may be doing it myself, if this isn't common knowledge: The Kwarazmians (No I have no idea how to pronounce it either) where a dynsasty that ruled over much of modern day central asia, Afghanistan, and Iran who OTL warred with the Mongols for three years in which they where utterly destroyed.