On Killing: The psychological cost of learning to kill in war and society, by Lt. Col. Dave Grossman

I read this book in hopes of getting some insight into the war atrocities that routinely accompanied the sack of cities in pre-modern warfare. This book, however, was surprisingly weak on war crimes. It's much better on the psychological barriers to killing in warfare, how such reluctance can be overcome, and what the long-term price is.

If anyone can direct me to the book I am really looking for, I'd appreciate it.