Which of the following best explains the difference between the way islamic caliphates dealt with conquered territories and the way christian states did during the post-classical era

Both, at the time period, operated somewhat similarly. The Christian states often used brutality against the "Non-believers" and so did the Islamic states, however, the main difference would be most likely the use of propaganda. During the Islamic "Jihads", the Muslims viewed the Christians as "infidels" while the Christians viewed their conquering as "Gods command"