Violence and Conflict in Genesis and Antigone

Violence and conflict have always been issues among animals and humans due to the instinct to survive and hack down whomever or whatever gets in the way. Violence and conflict are major themes in both Antigone and the book of Genesis. Antigone is laden with violent imagery; countless arguments causing conflict between Antigone and Creon as well as Creon and Haemon; and the blatant violence of the various murders and suicides present in the play. Genesis, on the other hand, has a range of stories; a handful of which contain large-scale violence, such as the destruction of Sodom and Gomorrah or Noah and the great flood. Genesis, as a much larger text than Antigone, also contains smaller violence, such as the story of Cain and Abel, which has one small episode of violence, or the story of Joseph, which contains smaller-scale violence but at a wider range.
Why is violence such a strong theme in both of these ancient works? Both Sophocles and the various writers of the Bible lived in more primitive times when there were weakly enforced written laws concerning justice and fair play. The common solution to most problems were along the lines of "an eye for an eye, a tooth for a tooth" which is a violent but sure method of justice. When Antigone buries her dead brother in the story of Sophocles's Antigone, Creon's immediate response is to have her killed and buried in response to the burial and her defiance to his decree.
However, when Cain murders his only brother, Abel, " The Lord answered him, ‘No: if anyone kills Cain, sevenfold vengeance will be exacted from him.' The Lord put a mark on Cain, so that anyone happening to meet him should not kill him" (Genesis, 4:15). The character of God isn't exactly loving or caring throughout the entire book of Genesis but he does, for some reason, save Cain from certain death for killing his own brother. Is this to teach Cain a lesson and have him live forever with his sin or is God saying it's morally just to murder