Societies should have some mutually agreed upon boundaries on conduct otherwise the society becomes a time bomb. There would be no functioning government laws or fair justice system because nobody would be able to agree on what should be outlawed or punished. There have to be if not rules guidelines and the either the majority or the people near the top of the chain of command would make those guidelines. That is an example of might makes right.

Some people have their own internal guidelines that they set for themselves, call it a moral compass, a conscience or voice of experience, there is a little voice inside everybody's head that says do or don't do that. You could say that it is keeping us from doing what we want by telling us what could happen, or in some cases what we are doing to the other person.

In the Pelopennisian Wars section I believe that the Athenians should have restrained themselves on the matter of the Melians, if nothing else than as a good faith gesture to show they mean no harm to the other islands. I can't help but think of those actions and the long term consequences. The act of standing down could work in the Athenians favor by giving them allies in the war against Sparta. The Melians could ally with the Spartans and rise up against the hold the Athenians who would lose lives and waste resources by trying to hold off an uprising that could have been avoided with a compromise. This isnt a naive gesture of fairness it is a calculated move that could work in the favor of all parties