Que? Rome was one big pile of civil wars and unrest. During the second century BC they had loads of social unrest, which for example paved the way for the military reforms of Marius. After that they had civil wars over and over again.

Anyway, RTW just isn't very suited for simulating civil wars. Unfortunate, since they were so important in history, but that's just the way the game was made. Perhaps EB4 or 5 will be based on a game that better models those things.