Read The Better Angels of Our Nature by Steven Pinker. It's a well-researched book that goes over how all kinds of violence (at least the easily-measured kinds)

Read The Better Angels of Our Nature by Steven Pinker. It's a well-researched book that goes over how all kinds of violence (at least the easily-measured kinds) have consistently fallen over time. This includes war as well as crime. There are local maxima, of course, but over any significant time scale and area, violence is down a lot.