Question

multiple-choice question
the ming dynasty added to the wall to keep out this group of nomads from the north.
mongols
japanese
romans
vikings

Explanation:

The Ming Dynasty faced persistent threats from northern nomadic groups, most notably the Mongols, who had previously ruled China as the Yuan Dynasty. The Ming expanded and fortified the Great Wall primarily to defend against Mongol raids. The other groups (Japanese, Romans, Vikings) were not the northern nomadic threat targeted by the Ming's wall expansions.

Answer:

Mongols