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?
In 1933, Albert Einstein inscribed a letter addressed to Sigmund Freud with the same title: Why War?*1 The physicist demanded to know, despite the advancement of modern science, how human beings are being urged to fight and kill their fellow being posed by wild enthusiasm. I wonder what Einstein would say, even after a century of even more advancement and civilization, the ubiquitous existence of war.
Throughout history, we have fought our way out of life. Though the initial fights and struggles were for food, shelter, and quality of life, as the advances in every aspect thrive, we did not stop there. Yet, we embarked upon fighting our fellow entities. Most of our ancient and medieval tales are grotesque and filled with pure vile. Even the ill successes and the insurmountable pains and traumas experienced for generations, don’t seem to suffice this lust we have for hatred and destruction.
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?
One might argue that wars are once declared for great ideologies. Even might add, for the good of the many. And yet, the majority (the poor, the non-ruling, and the common citizens) seem to pay the debt of the minority (the ruling class). In war, the poor die.*2 And even those who are returned from war are all dead, anyway.
I am, by no means, expecting a utopian world. Nor am I saying this because of naive optimism. But it is truly odd why we still believe in war. For one the mass destruction of cities and countries while creating a giant crack in the economy is sufficiently good reason for us to reconsider this mindset. If we were to speak in the manner of material losses and disasters.
Moreover, I would emphasize the intangible aches and scars imputed on all due to war. Without forgetting, nor diminishing, the physical disabilities and injuries most soldiers (and citizens) suffer from. Experts say that killing in war often triggers a moral conflict that can damage their self-image and relationships. Imagine the toll when it is civil war and the soldier is killing his neighbors. War traumas eminently cause depression, anxiety, increased suicide ideation, and post-traumatic stress disorder. The grief of the mothers for their lost children, the grieves of the kids for the loss of their parents, and the identity losses by all! Who or what could ever put a price to compensate for all these losses?!
While pondering on this idea a friend of mine said this for my untethering thoughts: “It is not that we choose war, we need war. The power balance is kept through the dominion of war.” Yes, war has infiltrated our minds in every way possible. We set out to kill and destroy. For dominance and upper hands, that is. The fact that most of our narratives, including movies and books, are infested by war stories is clear evidence that maybe war never infiltrated our thoughts and ideologies. It only surfaced from the depth of our being.
By the end of his letter, Einstein insists that any conflict can be rendered by discovering rather best ways other than cruel ways to kill others. And I agree. I would like to believe we can coin better systems and conflict resolution methods for the good of the many. After all, as General William Tecumseh Sherman said, War is Hell!
*1) https://en.unesco.org/courier/may-1985/why-war-letter-albert-einstein-sigmund-freud
*2) Confessions of the Lioness; Mia Cuoto [A Book]