Answer:
A) The need to find new grazing land for their herds, which were growing too quickly for available resources.
Step-by-step explanation:
The Mongol invasions under Chinggis Khan were largely driven by the need to find new grazing land for their rapidly expanding herds of livestock. As the Mongol population grew, their traditional grazing lands became overgrazed and could no longer support their herds. This led to a search for new grazing lands and ultimately to the expansion of Mongol territory through conquest. While the Mongols were also known for their religious tolerance and did not seek to spread a particular religion through their conquests, their expansion did bring about the spread of various religions across the territories they conquered.