Recently there were two articles regarding the long history of violence among humans.
Researchers studied the bone structure of australopiths, ape-like bipeds living 4m to 5m years ago which predated the modern human primate family Homo. They found that australopith faces and jaws were strongest in just those areas most likely to receive a blow from a fist.
US lead researcher Dr David Carrier, from the University of Utah, said the australopiths had hand proportions that allowed the formation of a fist, in effect turning the hand into a club.
Another article, far more recent in evolutionary terms, but before modern history, stonepages.com "5,000 years of violence in central Calfornia" "Chronicling 16,820 burials from 329 sites among 13 ethnographic groups, the most common type of violence was sharp-force trauma, caused by projectiles like arrows or atlatl darts - 7.2% of the sample. Another 4.3% suffered apparent blunt-force trauma to the head, while just under 1% showed evidence of dismemberment, with limbs, scalps, or heads removed after death"
Much of evolution is about survival, and survival strategies sometimes include violence. I wonder if social stratification is a form of violence, and squandering today's resources at the expense of tomorrow's generations, is violence against people who don't yet exist. wish we could learn to channel our violent tendencies in ways that are more productive. But with millions of years of evolution, maybe we can't.
Your last two questions are very good ones, most certainly worthy of investigation, philosophically if not scientifically.
I wonder if social stratification is a form of violence
I'm sure of it. It looks like a bloodless sort of violence, but it isn't. When applied stricty, it's enough to drive someone to suicide, because it isolates and denies people the place they need among equals. And it endangers their position - think of people in India's lowest caste, of women, of the have-nots and all the others...