Why Has Crime Dropped Tremendously Over the Past Two Decades?

David Brooks writes today that violent crime has dropped tremendously over the past couple of decades despite the fact that it's gotten easier and easier to buy a gun. So maybe we should focus on something other than guns:

Now we are in the middle of another debate about violence. If we lived in a purely rational society, this debate would have started with a series of questions: What explains the tremendous drop in violence? How can we build on recent efforts to bring the murder rate even lower? These general questions would have led to a series of more specific questions about police procedures, probably the most direct way to prevent shootings.

Call on me! I know the answer! Please, please, please.....

For a longer and more comprehensive take on this, I recommend Mark Kleiman's piece on crime and punishment in the current issue of Democracy. It's well worth a few minutes of your time.