The issue is inequality, not total wealth
“On almost every index of quality of life, or wellness, or deprivation, there is a gradient showing a strong correlation between a country’s level of economic inequality and its social outcomes. … This has nothing to do with total wealth or even the average per-capita income. America is one of the world’s richest nations, with among the highest figures for income per person, but has the lowest longevity of the developed nations, and a level of violence — murder, in particular — that is off the scale. Of all crimes, those involving violence are most closely related to high levels of inequality — within a country, within states and even within cities.”
— A review in the Guardian of The Spirit Level by Richard Wilkinson and Kate Pickett.