As Eric Michael Johnson writes for Scientific American, the biggest contributor to homicide in the U.S. is not mental illness, addictions or even the accessibility of guns. It’s economic disparity: the wider the gap between the rich and poor, the more violence a population breeds. Describing an analysis of homicide rates in 50 states conducted by Harvard’s Ichiro Kawachi, Johnson writes:
The results were unambiguous: when income inequality was higher, so was the rate of homicide. Income inequality alone explained 74% of the variance in murder rates and half of the aggravated assaults. However, social capital had an even stronger association and, by itself, accounted for 82% of homicides and 61% of assaults. Other factors such as unemployment, poverty, or number of high school graduates were only weakly associated and alcohol consumption had no connection to violent crime at all. A World Bank sponsored study subsequently confirmed these results on income inequality concluding that, worldwide, homicide and the unequal distribution of resources are inextricably tied.