J.W.

No, war is not inevitable. But also, the odds that humans will stop fighting wars, once and for all, is extraordinarily low.

"Why or why not?"

Simple: anything can happen. Peace on earth could last for a thousand years, or more, but then every next day would be a new day, with new unknowns, new opportunities, and new dangers - and that's sort of the point of being alive, if you ask me. You might have been looking for a more introspective answer, but that's the common sense one, as I see it.