Since I currently study pre-Civil War American history, I can't speak much on later topics such as the Nadir of American race relations (1880 ~ 1920), or the legacy of segregation & racism that reaches far beyond the 1960s. I also can't speak much on the treatment of history after that point, but I can provide some background to the actual truthfulness of those views.

While racial exploitation, violence, & discrimination have always been concentrated in the South, the North was hardly accepting of free blacks before the Civil War, & there was no lack of racial violence and segregation there in the 20th century.

But I have written before on the origins of racial discrimination, which should hardly be associated with a lack of education and poverty. The American South was the wealthiest slave society the world had ever seen, and racism was given justification by the wealthy elite, by pro-slavery intellectuals and the rich industrialist social Darwinists that followed.

To establish the inequality of poor farmers and wealthy plantation owners in the South:

Only around 1 in 3 white families owned slaves in the antebellum South, and a majority of those slaveholders had less than five slaves. A majority of slaves, however, were on much larger plantations, belonging to the narrow percentage of slaveholders with 50 slaves, or several hundred. We can easily compare the conditions of the average Southern farmer with say, George Washington, the wealthiest president who predates the 20-year rule, was a land speculator, owned thousands of acres and rented them out to poor tenant farmers, and had 300 slaves. (Jefferson, the essential Southern plantation figure, had the greatest number of any president, around 600?)

If you were a poor white farmer in the South, with no slaves, you did live in a society where slaveholding and racial inferiority were pervasive, and you probably aspired to own one. But, we should understand condition as one that is created by the wealthy plantation owners that made up the ruling class.

(If you were a poor Irish immigrant in the North, you would likely harbor resentment towards free blacks that you were competing with for labor. There were race riots & discriminatory laws. Most free blacks were rejected by the business class, and had no real hopes of entering the upper class of society & living a life of prosperity.)

The condition of poor whites & Southern farmers was slowly getting worse throughout the 1800s. The federal government, long before the Civil War, had an economic policy that was almost always favorable towards Northern business interests. Hamilton's program established a federal government that was rather explicitly intended to do interest-bearing for the rich, with the establishment of protectionist tariffs that were seen in the South as fees paid for the benefit of Northern manufacturing. For whatever hope you placed in the Jeffersonians, they had to absorb the Federalist program anyways, and Henry Clay's American System just tried to merge those business interests with more emotional appeal, and the promise of internal improvements for farmers. Jackson channeled some of that Southern/frontier backlash against Northern business interests, but could hardly prevent the rapid industrialization that was mostly taking place in the North.

After the Civil War, the Northerners were more in control of the national government than ever, & the South acted out mostly by antagonizing the North & terrorizing its black population. Meanwhile, industrialization and factory labor became widespread. During the Gilded Age, Southern farmers had this 40-year period of slow economic decline to look forward to, with a national government increasingly dominated by big business. This sets the stage pretty well for agrarian Populism, which is then absorbed into Progressivism and loses its agrarian character. If you are a poor, Southern white farmer in the 1800s, the future is dark. And you have poor blacks and wealthy Northerners to resent for it.

With that general understanding, you can better examine the treatment of racism, as it comes to be understood & discussed, in the 1900s.

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I can speculate on this, but the association of racism with poor whites, the depiction of rednecks as hopelessly conservative on social issues, and a liberal establishment that abandons poor whites & working class rhetoric, I would say emerged in the 60s and 70s.

This also lines up very well with the emergence of the white suburbs, and the professional middle class, which believes it is distinct from the inner-city working class. Northern Democrats like John Bartlow Martin warn JFK not to enter the Democratic primary in Indiana, because it is "redneck conservative country," and "suspicious of foreign entanglements, conservative in fiscal policy, and with a strong overlay of Southern segregationist sentiment."

Divorcing social issues and economic issues is the most important thing here.

And as the Democratic Party loses its grip on the working class, abandons the New Deal, and tries to pursue the professional middle class voter, (losing its economic basis), the Republican Party picks up the slack (but also centers on social issues). You see the Southern Strategy of Richard Nixon, the Moral Majority of the Reagan Era, and the association of populism with the racist & religious character of the new conservative movement, while liberalism takes on a more well-educated & diversity-oriented, yet corporate elitist character.

In the 1990s, (and I know I am dangerously close to the 20 Year Rule), you see the Democratic Party complete this transition, with the Third Way ideology of Bill Clinton, "socially liberal & economically conservative." They try to adopt a tougher stance on crime, on foreign policy, and this creates some level of conservative consensus. With two economically conservative parties, there is growing inequality, corporate consolidation, NAFTA has a huge negative impact on rural America, and they no longer have a real change in material conditions to offer working-class voters.

The party of Jimmy Carter in the 70's and Bill Clinton in the 90's has become far more moralizing, There's a backlash to political correctness & diversity politics. And the cultural division paints over the economic consensus. The Southern "socially conservative" identity is weaponized by the Culture War which has been waged since the 80s, and a focus on asthetic politics essentially pushes out discussions of inequality and economic insecurity.

I might be showing my bias here, but that would be my explanation for the sort of "redneck resentment" in modern American politics.

I definitely cannot go into as much detail as the person who previously commented, but I think this needs a lot of discussion about how the US North and South became so drastically opposed, and why exactly the South is more scrutinized for racism.

Before the slave trade, both the north and the south made use of indentured servants instead of actual slaves (aside from the few places that were still trying to enslave Natives, which wasn’t working very well). These would be poor people also coming from Europe who offered up their services to a household for so many years in exchange for free travel to the New World. When their time ended, they would be free and able to supposedly pursue the same opportunities as anyone else coming to America. Once the slave trade began, however, indentured servants swiftly became replaced with slaves that were indebted to you for life. The North only used them for household duties and would maybe only have 1 or 2, if they could afford it. The South realized they could use many slaves to do their farming work, and they wouldn’t have to pay for the labor that they did. The geography of the North made it impossible to do any large-scale farming so owning dozens of slaves was a waste of money. The South could profit off of it, though, and produce 50-100x the amount as a small farm. Plantations took advantage of this for crops in the South that were in huge demand, like cotton and tobacco.

So the extremely wealthy people in the South would arguably be the most racist. They were the ones up to the Civil War defending their right to own slaves, and used all sorts of racist ideology to uphold it, but their real motive was making sure they got to keep the amount of money they were currently making from not having to pay slaves. The North was quicker to abolish slavery because they never needed slaves, not that they were any less racist than the South. Abraham Lincoln himself said that whites were clearly the superior race, but that he believed every race should have equal opportunity in America. Of course, anyone today would easily be able to argue that you can never give black people the same opportunities if you don’t believe that they’re equal to you.

I believe there was even a time when poor, Southern whites were against slavery. They were the ones with small farms that could never compete with the plantations. However, they would probably be discredited simply for a lack of wealth and education. I think the South had to work hard to get them on their side by the time the Civil War started, by championing “states rights” for the South as their cause instead and fear-mongering a crash in the economy for the South if slavery were to be abolished.

The North/South divide was because of who had abolished slavery and who had not, but not exactly because of who was less racist and who was not. However, if you could be a free black person in the North, that was a shit ton better than being a slave in the South.

This divide becomes even worse after the Civil War, though. The South is basically destroyed, is forced to rejoin the Union, and is going to harbor a lot of resentment to the North for no longer having slaves and having to see them as actual people. Let’s remember how much racist propaganda was poured specifically into the South so they could view them as property and not feel guilt for keeping them as slaves. The South absolutely hates the North during Reconstruction, and there isn’t really a difference between the ideas of wealthy Southern whites and poor Southern whites at this point. Poor whites are even worried that free black people will be able to overtake them in the social structure. They want to do everything they can to keep them in subservient positions, and plantations still need workers—so now you enter the share-cropping and Jim Crow era of the South.

Jim Crow is undeniably what shapes this idea of the South as racist and the North as not. The turn of the century is experiencing a switch in the political parties because of industrialism—Republicans now want less federal government intervention, Democrats want more. The South make up all kind of rules to keep black people as second-class citizens. Federal law now states black people are allowed to vote. Okay, the South says, so what if we say you have to prove to be able to read to vote? To pay to vote? To not have slave ancestors to be able to vote? They make up laws like loitering to arrest black people for petty reasons, because there’s a loophole in the 13th amendment: you can still keep people as slaves as punishment for a crime. You can get black people to do labor for you as long as they’re prisoners. These are all South, state laws, and don’t exist in the North.

Segregation still exists all across the country, and there’s no doubt white people even in the North don’t want to co-exist with black people. White flight, like you mentioned, is a great example of this. Race riots are not a product of one geographic region, and I feel like they’re actually underplayed in the South. Any place in the South that was able to boast a society of middle-class black people ended up being rioted and destroyed by white people post-Civil War. I think the big difference is the South was paranoid about black people gaining steps in the social hierarchy, while the North just wanted to stay segregated. The idea of “separate but equal” was upheld by the federal government until Brown v. Board of Education.

There’s a reason the Civil Rights movement was so highly concentrated in the South. The North was still more willing to integrate than the South was, and again, Jim Crow didn’t really exist there. Black people never fled to the North in waves like most people expected them to; their families and everyone they ever knew lived in the South, while most never had the financial capabilities to uproot their life. So you still had higher populations of black people in the South than in the North, and the South were entirely more aggressive in trying to keep them in lower positions.

The Civil Rights movement convinces a lot of more moderate people across the country to care about rights for black people. It becomes shameful to be racist (I personally think this is when white people become unable to admit that they can be racist, because a lot can’t distinguish between active and passive racism) so people in government try as hard as they can not to show that they were actually racist. Democrats had been in power for years, so when it comes to Nixon’s candidacy he focuses on gaining Republican support in the South. One of Nixon’s aids has admitted that their entire strategy was to get white people on their side by appealing to their internal racist thoughts, without actually saying something racist. There’s a tape of him saying “well you can’t say n***** anymore, so instead you say something else” (I forget exactly what he said). Nixon and Reagan effectively switch the South to Republican states, all on racist ideology. Even Democrats have to appeal to the Republicans “tough on crime” and “war on drugs” policies to have a chance of winning, even though all reports and studies show these policies 1) don’t work and 2) disproportionately affect black people. It’s safe to say that even the not-racist Northerners had political beliefs that were damaging to black people.

I know you want to abide by the 20 year rule, but I think it’s important to mention that the poor, uneducated, racist white southerner stereotype is more of a product of recent times. Like I mentioned, the South was more aggressive in racist policy, and so a lot of people that are stuck in conservative tradition are way more vocally racist than others. There is also a trend in which the more education you receive, the more likely you are to lean left on political views. Southern rural areas tend to be the least educated, and have the worst education systems overall, in the country. I don’t want to paint this as being just a characteristic of the South, though, because a lot of this is largely due to class inequality that affects education.

To answer your question, I think there is some validity. We can’t ignore the violent and racist past of white Southerners, but I definitely agree we need to focus more on how racism was an ideology that grew from slavery and didn’t just go away because one place didn’t have slaves or once slavery was abolished. I think, especially when we learn about the Civil Rights movement, there is a focus that the South perpetuated all of it and once LBJ signed the Voting Rights Act it was all okay. No more racism! It’s both an effort to maintain that racism existed only in one place and that people nowadays aren’t racist anymore.

The history of The Populist Party in the USA is also very interesting in regards to this topic. It tried to appeal to poor white and black farmers and was successful for a while. It’s policies based on class rather than race. It’s message was popular and reached across race lines. But the Democrats, whose voters The Populist were stealing, decided to emphasis and play the race card and the old divide and rule. Their message to poor White folk was - I paraphrase - you’re poor but at least you are not black. Fear of The Populist Party and the fact it might get seats because of their black voters was one of the reasons that voter alienation laws were bought in, so that blacks could no longer vote. Black folk gained the right to vote after the war and did so for a number of years, but this right was slowly taken away from them from 1877 onwards, using things like the Grandfather clause and literacy rules. After the defeat of 1896, white Populists slowly drifted back to the Democratic Party. Black voters lost their right to vote and only regained it in 1964.