There is no justification for murder. Murder is killing by applying offensive force, it can't be justified. Don't try to. Thank you for surprising me and actually admitting it's murder though, I didn't think you would.
You (and millions of others) are guilty of collectivist thinking and inadvertently answered your own question why there are wars. It has to do with your unfailing obedience and reverence for false authority. Take your learned obedience etc. and scale it up a few million people and you have created the recipe for war. I could go into detail, why your indoctrinated mindset is the root of the problem, but I want to savor your trying to justify murder for a while.
Not trying to be a dick, but you have much to unlearn.