Why War?

Is there an inherent propensity to take upon arms and collectively kill? Do we, perhaps, lust for war? Or is it just an odd craving we could never satisfy?
*1) https://en.unesco.org/courier/may-1985/why-war-letter-albert-einstein-sigmund-freud
*2) Confessions of the Lioness; Mia Cuoto [A Book]