I am optimistic enough to believe that humankind will eventually evolve to a state where we all live in relative peace with one another. By relative peace I mean that the recourse to violence on a national scale will come to an end. I'm not saying it's going to happen in this century, but I expect by the end of the next one it will.
The shift towards more real community belongingness among all people will gradually take hold as the world 'shinks' in size psychologically. The 'them and us' will give way to 'we' who reside on planet earth. Of course,by that time we might have a few colonies living on such places as the Moon or in huge artificial satellites which orbit the various planets of our solar system. Those pioneers might not like to be regarded as 'earthlings' if they happen to be second or third generation Moon people.
The pessimists say we'll never have world peace. Such do not only see their glass as half empty but worry about the chlorine in the water. Optimists such as myself take a different view. Our 'cup not only runneth over it has beer suds atop of it. Of course we humans will get beyond war and deliberate killing and the worse types of crime. It is just a matter of time.