I’m afraid I’m going to have to disagree strongly here.
There is never a need for war, it’s a complete failure in human terms. Anyway, just because something has always existed, doesn’t mean that it should continue to exist or that there is any mitigation on our part – thievery, murder, lying, unkindness, suffering and greed have always existed, that doesn’t mean we just shrug and say that’s how things are – sort of like what the whole message that Siddhārtha Gautama Buddha, Zoroaster, Jesus Christ and others have been trying to get through our thick skulls since time immemorial, which, leaving aside the divine or theology, shows that people long ago in the past realised that this was not a good way of being just as much as (some) people do today.
As an aside, the historical druids – at least what we know of them, formed a separate class or caste from the warrior-aristocracy and the farmers in Celtic societies, so I don’t really think there were “druidistic warriors and farmers” and whatnot, and this model would pretty much fit with what we know of Indo-European (culture) societies in the ancient world from Galway to Bengal.
Furthermore, one would hope that we had, as a species, somewhat progressed from the early Iron Age, and, certainly would not seek to justify our own behaviour because of that of our relatives in ancient times nor our more distant ones in the primate world – DNA is not a justification – we share approximately 50% of our DNA with bananas, that doesn’t really say much, though, does it?