Really it was troop rebellion as the troops farther from Rome would obey their officers more than head command. The barbarians also where instrumental in the fall of Rome
Geographic means physicals features of the land in this case you look at only the negatives of this like big bodies of water mountains and steep terrain these made it difficult because some settlers didn't have horses or were traveling in large groups wich could contain elderly and young children
I believe that the answer is D.
