Yeah, some time in the Stone Age, those innocent days of honorable slaughter as men killed men and then ate them... ah, those were the days
They had rituals and duels, that does not
make them some paragons of what we'd consider virtue today.
They happily killed and raped and did underhanded things to each other, just like everybody else, besides being pederasts and slavers and a bunch of other things we don't approve of; but, like the 'laws of war' that we have today, they had little rules about how it worked, is all. Like a lot of the African tribes, they fought wars at least partially for ritualistic reasons, and did not always fight what a modern person would consider a "war", where territory permanently changed hands, etc.