Of course the healthiest, happiest parts of the nation seem to be the whitest parts: The Upper Midwest and New England.
These areas are where close community ties and economic security are strongest. The difference between the neighborhood in Bismarck, North Dakota and the neighborhood in Jackson, Mississippi is that the North Dakotans have much less poverty. When you greatly reduce the number of impoverished, the inequality of the non-impoverished becomes less apparent as well.
This "sameness" that allows you to relate to your neighbors both culturally and economically also fosters more altruism and neighborly help.
Sure, there are still wealthy people around... but they don't look as wealthy by comparison. Instead you might have a neighborhood where most homes are 3 bedrooms but the rich guys live on the lake in a 5 bedroom house and THEY HAVE A WATER TRAMPOLINE!!!. And you know this because your son is best friends with his son.
I think int he impoverished areas there's this sense of competition and stratification where communities congeal much more along non-economic lines which ultimately reduces upward mobility.
History is important in this regard too. The Southern United States' entire social system was based on a small number of incredibly wealthy people controlling the impoverished masses through the economic systems of slavery and tenant farming. That legacy is important even today.
That is true to an extant, but a lot of the most impoverished areas are in the Upland South, where there were few if any large plantations and race was not as prominent with far fewer blacks.
