Simplify the following text for a Grade 12 native English-speaking person.
Original: Whereas the reign of Marcus Aurelius had been marked by almost continuous warfare , even though he preferred books over war , that of Commodus was comparatively peaceful in the military sense but was marked by political strife and the increasingly arbitrary and capricious behavior of the emperor himself .
Simplified: The reign of Marcus Aurelius had been marked by almost continuous warfare , even though he preferred books to war . That of Commodus was comparatively peaceful in the military sense but was marked by political strife , and the arbitrary and capricious behavior of the emperor himself .