I honestly believe that peace is our true nature. The thing that prevents this from being reality are illusions that make society look like we are different and separated from one another. If there were ten people (living together) on the earth, those ten people will not have war. They will have conflict, but they will not have an argument that cannot be resolved by understanding, and the reason is that they are that close to each other that they have discovered a love for each other.
The reason I beleive this is because we are happy in peace and unhappy in war. If we were naturally inclined to war and conflict I think that nature would show them as being desirable and making us happy. If we recognized the love we are capable of having for even our greatest enemy, then greed and war would not be issues, because we would have this feeling of compassion for everyone, and not want to suffer. That's clear thinking, but it's so hard to do! Since our birth we've been taught that there is an "us" and a "them." I think that psychologically we will eventually evolve into beings who respect and cooperate with each other.
~peace~
EDIT: I just wanted to add that the way that we acheive our true nature is to recognize love inside ourselves, which we have for others that are like us. The segregation in the world prevents us from this realization. When those barriers are broken, and society has a great feeling of love for each other, there will still be conflict but it will be rarer and rarer. By this time, many diseases will be cured and that goes for mental diseases too, which can include anti-social behavior. It's not as if capitalism will fall and this will happen all of a sudden, but if the world created a cooperative socialist system it will be a giant leap forward.
If you look at it in an evolutionary way, just look at the way parents raise their children today. Generally speaking, it is a much more humanistic approach than even 15 years ago (no more beatings, a stronger-than-ever appreciation of children as emotional and intelligent beings). These people who were given love as children will be more likely to be able to give love as adults to other adults, and therefore they will reproduce and raise their offspring to an even more compassionate way. Humanity will grow smarter through natural selection because love is more "fit" than hostility.
I have no doubt that we CAN acheive this. The only thing I'm afraid of is that we destroy ourselves before we ever get there.