Actually you can't conclude that - you can conclude that there may or may not have been war but based on the evidence available it seems that there was no war. War leaves tell-tale evidence of destruction, but there is none. It seems a very reasonable theory (unless proved wrong) that they didn't need to go to war.
As there were no invading outsiders it seems one reason, but also they didn't fight amongst themselves which is strange.
Fighting, competition, ambition, defense of one's own family/estate, argument, misunderstanding, physicality, testosterone/manliness, love (two or more men loving the same woman), jealousy.
Those are just a few of the things I toss out there to suggest that the absence of war (large or small) is impossible over a protracted period of time.
Like it or not, fighting is just human nature.
In fact, it is the threat of violence that helps maintain the peace.