I just found this article. I don't know that it's a terribly new idea - it cites books that were mostly written in the 80s and 90s - and I'd heard it mentioned before, but never read too much about it.
tl:dr; the article argues that children raised in physically, emotionally and/or sexually abusive environments have underdeveloped brains which lead, among other things, to a lack of empathy and a perpetuation of violence on a society-wide level - that is, to war. It uses examples from Germany pre-WWII and some violent New Guinean tribes. I think it's interesting and plausible, but my anecdotal evidence only halfway supports the idea.
As a child who was emotionally abused and beaten bare-bottomed with a willow branch, and who grew up around a lot of abuse, I obviously can't tell if my brain is underdeveloped, but I feel like I'm less prone to violence, not more. However, maybe it also means "prone to accepting violence as normal" - like I wrote yesterday, being abused was almost addictive when I was in an abusive relationship. Almost every single one of my closest friends has also experienced some form of abuse - maybe I wouldn't even realize it. I do know the Abusive Asshole was raised in a ridiculously abusive household, where he was not only abused himself but was regularly exposed to violence perpetrated against others, particularly women. I used this as an excuse for his behavior many, many times.
So if it is true, how do we stop the cycle, other than raising our children to be healthy? What do we do about the millions of people who were abused as children? how can we ever fix that? How can we help those still stuck in the cycle without making excuses for their behavior?
Oh, and as a side note, I feel a little uncomfortable about the way the article discussed New Guinean tribes. I assume what the author wrote is true, and if so it's pretty fucking horrifying, but I feel like there's also a long tradition of white people going to remote areas like New Guinea and talking about native peoples in really racist and othering ways.