"It's almost like the Romans put violence and murder up front in all their stories."

Well.. Let's face it, they weren't the only ones..LOL. Remember the Atrides? Or Oedipus? Not only murder, but incest.
Stories of interdynastic strife and murder abound in history. The Borgia...
The germanic practice of kingdoms being split between brothers at the father's death yielded some interesting results too..
At least, Romulus didn't kill Remus while he sought protection in his mother's arms, like Caracalla did to his brother Geta. Tacitus summed it up magnificently, as usual: "Insociabile regnum".
Actually, the story of the rape of the Sabines, for instance, although beginning with violence, does not end up in general mayhem but in mixing up of two populations (due to the Sabine women's wise intervention..) and that is a first.
Needless to say, that episode has been explained in detail by anthropology and has to do with a natural protection mechanism that keeps primitives --hence fragile--societies from destroying each other in total warfare.
Either through a ritualisation --regulation-- of warfare which results in fewer people killed and in some cases only in a couple of broken bones, or through outside intervention, like the wise elders of the tribe... Or the women.
Another must read: John Keegan, "A History of Warfare". He explains all that most brilliantmy.