Heavily influenced by both Leviathan and Nietszche. I believe we created the concept of good and evil, it's a consequence of developing reason and conscience, we attributed values to things and certain "natural laws" that act as a kind of common sense, usually dictated by a divine entity (some kind of imposed divine law that a group of people simply will not argue about), or as I said, the consciousness of a given people. In that prism we are neither inherently good nor evil. But as put in The Leviathan, and I believe it makes much sense to the point I'm inclined to believe in that, all those natural laws only exist because we're inherently evil/greedy, imagine that, maybe due to animal instinct individual A always breaks into individual B's land until he finally manages to take the land form himself, A does that because he is stronger, and one day C arrives and takes A lands, C is very powerful and moves on to take that which belongs to D, but D is also strong, it ultimately loses, but the effort has tired C so much that now E, a much weaker opponent can easily take over C. Soon they all realize that they could choose a sovereign, who would impose rules to define, in this case, property, the ruler would probably be the strongest of them, the only thing impeding this ruler from being a total tyrant being the fact that everyone together could topple him (a sort of impeachment). In other words, everyone reaches a consensus about a ruler and laws (positive laws, not natural laws), not because they're happy to play ball, but because it is convenient, and makes it easier on everyone: basically you don't solve your problems by crashing your adversaries skull to a rock because you're a good guy, but because you don't want to go to jail (which could take me to the discussion of moralism by Kant, but that's another discussion).
Look at PUBLIC International Law, there are four major theories on that, and I'm gonna concentrate on the one I believe in, it's called "Realist Theory", it was born with the end of World War I, the League of Nations was created and the idea was basically "no more wars, only reasonable men fighting with words to achieve what's better for their country and the world". The followers of such theory would say that the League of Nations would fail, simply because "The International law is a fraud, when it comes to international relations all there really is is ANARCHY", they were proven right with the end of the League and the ascension of the Third Reich and, obviously, World War II. It's pretty basic: Germany had signed all treaties that made it weak and threw on it every blame for WWI, but they said that Germany wouldn't care for the treaties, no country would, as soon as a treaty got in their way, if they could take whatever they wanted by force, then they would, to hell with any treaties. And that's exactly what happened. I dare say it's exactly what HAPPENS. Look at the UN, it's a joke when it comes to regulating wars, they said "USA shall not wage war on Iraq", USA replied "Fuck off, I'm stronger, and I will" and they did*, and this can spread to every type of behavior, you can take that to society level, we follow the law, but when WE think it's not very nice, we break it, it might be very minor, like the car stopped in a non-stop area for just a few minutes, so you can buy the ice cream and get home in time to watch soccer. It all indicates, that deep within we are "evil" or at least, savages, and we only follow rules because not doing so would mean the destruction of so many of those of us who just aren't as strong as the rest, it would mean so much "trouble", for that we lie about being free, because no one is really free while there are laws around, thus true freedom is something very very scary.
*= don't want anyone getting touchy by it, but it's a fact, particularly, I love the USA, and believe Bush did what he did thinking it was the best for his country, it might have had ZERO diplomatic and political "elegance", but that's not for me to judge, I wasn't affected by the war and I hate hypocrites who stand universes away from the battlefield (or direct consequences) and feel in the right to comment for or against it.