Via Andrew, Radley Balko floats a theory:
In his 2004 book A History of Force, the Independence Institute economist James L. Payne argues that during the last few centuries, deaths from all forms of human violence--war, ritual killing, state executions, homicide, and so on--have shown a remarkable decline. Payne attributes this trend to a dramatic rise in global standards of living, particularly after the industrial revolution. Our lives are more valuable now. Harvard cognitive scientist Steven Pinker covered similar ground in a fascinating and counterintuitive 2007 lecture for the TED Talk series.
The same phenomenon Payne and Pinker describe globally could be what's happening here in America. In his 2000 book It's Getting Better All the Time, the late economist Julian Simon documented the remarkable, historic improvement in Americans' standard of living, especially among the poor, during the last several generations. These improvements, unlike fluctuations in economic growth or the stock market, tend to be a one-way ratchet. The fact that 80 percent of poor households now have air conditioning, for example, is an astounding development; in 1970 just 36 percent of all households did. Perhaps not incidentally, homicides tend to rise with the temperature.
We live longer, more comfortably, more richly, and with more leisure than ever before. During the same period when the crime rate has dropped, other social indicators also have shown remarkable improvement: Rates of abortion, divorce, and teen pregnancy in America have all plummeted since the early 1990s. It seems that as we live better...we live better. The crime rate has continued to drop even in the most recent recession, though the drop has slowed. But while recessions obviously make life more difficult for many people, they don't walk back the broader standard-of-living trends that Simon describes....
I would like to see this broken out more across different demographics, and not just race. I do think that it's often easy to overlook what poverty looks like in 2011 and what poverty looked like in 1811. Or even what it looks like in other countries.