I don't believe there was ever a year in human history when there was no war going on someplace.

Honestly, it's sad how much that makes sense.

maybe the natural state of mankind isn't war nor peace, but perfectly balanced as all things should be

Hmm, interesting question. I would say we are always in some kind of fight, whether it's fighting for your country or making sure your family has food to eat. We will do everything we can to make sure our family and friends are safe, taken care of, and overall better off. To do that, you need to fight.

It is possible. There are variety of monkeys whose temperaments have been demonstrated to be inherently greedy, territorial and physically aggressive with their own kind. So if animals can be born that way, who is to say man is not?

For fallen man, sin is the default,
But for born-again man, Godliness is normal, and sin an abhorrent anomaly.