I ran across an interesting quote by linguist Steven Pinker in the july 5th issue of New Scientist:
“My next book will be on the decline of violence and its implications. Rates of murder, warfare, genocide, torture and deadly riots are lower now than at any moment in human history. Assuming that we have’t changed biologically, then what has changed in our psychology and soceity to make that possible?”
The interview went on to suggest several reasonable possibilities, including the spread of the concept of a fair and impartial judiciary but left out two which I think may be very important: wealth and freedom.