My personal opinion is that humans are quintessentially self-destructive. Let's leave out religion since it seems to be a very, very superficial cause of the "un-peace" now.
We're not only, warring amongst ourselves. We're destroying the earth, our very own habitat that keeps us alive. We cause extinction in other species for our own selfish purposes.
In short, the Sentinel in The Matrix made a very relevant point. "Human's are a virus". We spread and spread, have not much care for our external environment and we use up the environment around us like it is there forever.
Some people will refuse to believe we are the worst of the animalia family. Our brain/mind is a double-edged sword. It brought us innovation and progress but it will also be and it is our downfall.
I guarantee there will be more people who disagree with me then the total number of alphabets in this post. Peace is a facade. Bonafide peace will never be attainable or sustainable.