Diversity breeds murder, inequality does not: A standard finding in criminological research is that homicide is strongly related to inequality: in societies with a big gap between the wealthy and the poor, the poor become resentful and take it out on nearby targets, also poor. This theory always seemed a bit of a stretch to me, the idea that I hate how the Man is screwing me, so I kill some guy at the bar for calling me queer. The theory turned every fist fight into something political. But the macrolevel correlation has been very reliable and very strong, I admit. A little investigation of mine evidently explains what is going on. Past cross-national studies always had a handful of Latin American countries with soaring homicide rates, and we all know that part of world reigns supreme in the rich-poor gap. So these outliers basically determined the size of the correlations. And yes, Latin murders are frequently political and tied to inequality.
But the whole situation changes with the sample I just constructed. I gathered the most recent homicide data for all countries that have published it. Data is now available from all the former Soviet countries. These are relatively equal countries, many of which have horrible violence of the organized crime type. When they are included in the analysis, the inequality-homicide link disappears.
Ethnic heterogenity, on the other hand, does have a significant influence on violence. The correlation between it and male homicide victmization rates is .41; for female victims, it's .48. Diversity breeds distrust and conflict, and can even lead to murder.