At a writers conference last year, thriller author Sarah K. Stephens and I had a great conversation about violent historical patterns. I mentioned that I'd heard someone suggest that the number of US serial killers in the 80s might have something to do with their being raised in post-WWII households by traumatized parents, but Sarah, a developmental psychologist, warned that "root causes" didn't tell the whole story. In her field, for example, violence is being studied as con