America’s law enforcement system has seen a number of successes over the past few decades. The major crime wave that began half a century ago has been somewhat reversed. After surging in the 1960s and 70s, gun homicides are down by 49% since their peak in 1993, and non-fatal violent crimes in general are down by a remarkable 72% over the same period. Property crimes (burglary, theft, etc.) have also gone down, dropping by 61% from 1993 to 2011.
There are a variety of theories about the cause(s) for this decline in crime, but there is still no consensus. In a number of cases, however, localized declines in crime can be traced directly to new policing techniques that serve to discourage crimes before they happen. (E.g., New York City went from one of the most dangerous large cities in the US to the safest, in large part because of a major investment in increased high quality community-based policing that reduced all crimes.) Other possible contributors to the nation-wide drop include changes in demography, technology (computers, cctv, and now cell phones), incarceration rates, and social values. http://www.pewsocialtrends.org/2013/05/07/gun-homicide-rate-down-49-since-1993-peak-public-unaware/=
However, despite the successes in crime reduction, violent crime is still higher than it was in 1958 and much higher than it has been in Canada (the most similar nation) at any time in the last half century [Pinker, p. 117], so we can’t rest on these achievements.