Law is just something we create to give perceived order which allows enough peace for people to do things they need to do to live. Nothing is written in stone. People are not treated equally in any country including the US. We cannot control minds or reprogram people to all think and act the same. Even in brainwashed North Korea, there is only surface obedience and of course those who oppress there do not follow their own rules.
As for military intervention, you could have any reason to do it. If you are threatened by another group why would you want to let that threat remain. In the case of North Korea and South Korea both parties have the right to strike as they are both threatened by the other. The US also has the right to strike now that there is a threat of weapons reaching US soil.
Right and wrong are subjective. We are merely animals when it comes down to it. We can live by whatever rules we chose. Often though we live under some else's rules. Are you really free living in a world that is to your perfection? If not are you wrong in your thoughts when you feel something is not right? Everything is up for reinterpretation even the idea that we exist in the first place.