Poverty is a national thing, easily found in rural and urban areas. Wealth, however, tends to be more of an urban phenomenon. The South is inherently disadvantaged because of the aforementioned lack of major urban centers.
If you look at where poverty is concentrated, it's in the South but it's also in the Rocky Mountain West and the lower Midwest.
If you get to a county-level breakdown, there's two areas which drag down the South overall: eastern Kentucky and the Mississippi Delta (along the Mississippi border with Arkansas and Louisiana). I've been to both areas, and yes...they are some godforsaken places.
Vicksburg, MS was just a depressing city to visit. Actually, the whole state of Mississippi was a depressing study in poverty and, for lack of a better word, abandonment.
Eastern Kentucky is the purest distillation of Appalachia -- mountainous, wooded, sparsely populated, but unsuitable for any large-scale agriculture. There's also enough meth labs, pockets of marijuana fields and even old-fashioned bootlegging to keep the Justice Department busy for decades. Makes sense, when the unemployment rates are typically over 14%. Gotta make money somehow.
But if you look at South Dakota, there are chunks that are even worse. Without even looking, I can tell you those are Native American reservations. I've been there too. They make the South look like the land of plenty. Unemployment rates that top 80% in some cases like the Oglala Sioux (89%) and Cheyenne River Sioux (88%).
If you look at the "New South" (a crescent running from central NC through upstate SC, northern Georgia, northern Alabama and central TN) it actually compares favorably to the Great Lakes region and the Eastern Seaboard in terms of poverty rate.
As to the racism bit -- they say that familiarity breeds contempt, but to truly hate someone, you have to be distant enough to dehumanize them. The African-American population in the South has always been higher than anywhere else in the US, with the exception of major cities like New York, Baltimore and Philadelphia. There's a low-level racism that permeates a lot of the South, based on socio-economic divides as much as anything. Many middle- and upper-class people who might look down on poor blacks look down on poor whites just as much. Poor whites look down on poor blacks because it's about the only demographic they CAN look down on, and because the rhetoric from the Right is that these "lazy blacks" and their "liberal white elite" allies are conspiring to keep poor white folk down. And even then, when you get right down to it, a LOT of poor whites get along with their poor black neighbors just fine. Because when you're poor as shit, anybody else that is too might as well be your friend.
If you look at the history of the Klan and other white supremacy movements in the US, their core isn't in the South, it's the upper Ohio Valley. Indiana was the epicenter of white power in the 1920s, and a swath from Illinois to New Hampshire remains a hotbed of Neo-Nazi/white supremacy activity, as does California.
NY Times did a story last year on Stormfront.org (the Facebook of the Neo-Nazi movement), and the demographics of its members. Surprise...they're not a bunch of Dixie rednecks.