Organized group warfare? Do you mean bar fights or nation-states and insurgents? What proportion of humans take part in acts of organized group warfare? Saying war is natural to humans is to selectively ignore that the vast majority seem to prefer peace and/or don't have time for the war games.
The decisions and designs of organized group warfare are in the hands of an extremely small few and they are constantly trying to balance the application of their wealth between keeping domestic subversion at bay while clumsily dumping bombs and bodies around the world to "preserve peace."
War is not an undeniable urge, it's a choice. It's proven morally corrupt in most recent applications and this searching for some innate reasoning is an attempt to give hawks a way out of their cognitive dissonance. It's killing for duty, profit, and fun. You always have a choice.
Bonobos' reputation as make-love-not-war pacifists is quickly becoming undermined by recent research. They hunt for meat, go months without sex, and engage in (albeit more limited) intergroup conflict.
Examining Pan paniscus and Pan troglodytes are like looking at exaggerated aspects of our own nature. But in looking at the behavior of humans, organized group warfare appears to be the norm, rather than the exception.