What drives white Southerners' support for Republicans today? A new study, to be published in the Journal of Politics later this year, suggests it's not only modern issues, education, age, and racial demographics — but also the state of slavery in 1860.

The study, from political scientists Avidit Acharya, Matthew Blackwell, and Maya Sen, analyzed historical and survey data ranging from the 19th century to the 2010s, looking particularly at the local prevalence of slavery in 1860 but also at several other variables to gauge their possible impact on modern political views.

The authors concluded that "the local prevalence of slavery — an institution that was abolished 150 years ago — has a detectable effect on present-day political attitudes in the American South." Specifically, in areas where slavery was more common 150 years ago, people who live in those same areas now are more conservative and harbor more racial resentment.

To some extent, the findings reiterate something we already know. Republicans have, after all, for decades tapped into many white Southerners' racism to garner support — through the well-known "Southern strategy." But the paper provides some insight into why this strategy has worked.

What the paper found

Acharya, Blackwell, and Sen drew on a sample of more than 40,000 white Southerners, along with historical census records, to evaluate how political attitudes vary in counties that had more slaves back in 1860. The result: There was a strong connection.

"In areas that had higher slavery in the 1860s, those areas have whites living there today that are more conservative overall," Blackwell told me. "They're more likely to identify with the Republican Party. And they're also more conservative on what we might call race-related issues — things like affirmative action and measures from psychology and political science that are designed to figure out what people sometimes call racial resentment."

As this chart shows, the prevalence of slavery in 1860 correlates with present-day Republican affiliation, opposition to affirmative action, racial resentment (based on two questions that gauge how white people feel about black people's ability to "work their way out of the lower class"), and contemporary white Southerners' negative feelings for black people compared with white people (based on a "feeling thermometer" score):

With this kind of correlation, it's always possible there are some other causes driving the findings. After all, correlation isn't always causation.

But the authors controlled for several potential explanations, finding they didn't explain away the link between slavery and modern political views. They looked at economic and social conditions, geography, population shifts, present-day racial demographics, and more — and none fully broke the link. (The full data is available in the study.)

It's of course possible that the study missed some confounding variables. But the study deployed some fairly rigorous controls, so its findings appear reliable.

So what's the reason for the connection? The authors suggest that the end of slavery had a tremendous, lasting impact on white Southerners that's been passed down from generation to generation:

For example, Key (1949), Du Bois (1935), and Foner (2011) (among others) have argued that the sudden enfranchisement of blacks was politically threatening to whites, who for centuries had enjoyed exclusive political power. In addition, the emancipation of Southern slaves undermined whites' economic power by abruptly increasing black wages, raising labor costs, and threatening the viability of the Southern plantation economy. … Taken in tandem with massive preexisting racial hostility throughout the South, these political and economic changes gave Southern Black Belt elites an incentive to further promote existing anti-black sentiment in their local communities by encouraging violence towards blacks and racist attitudes and policies.

To test this idea, the authors looked at how the adoption of tractors in some counties affected anti-black attitudes. The idea: If white Southerners could use the technology to mitigate their demand for black labor and maintain economic dominance over their black counterparts, there would be less of a need for anti-black attitudes to maintain white supremacy.

The hypothesis held true: White Southerners in counties that adopted tractors earlier were less likely to hold anti-black and conservative views today.

Based on the findings, it seems anti-black attitudes have been a way for some white Southerners to keep white supremacy in their counties after they struggled to adapt to political and economic losses once slavery ended. And such attitudes remain today — through modern political views — as a way to maintain white Southerners' political and economic dominance over their black counterparts.

One caveat: The study also found the effect of slavery falling over time — it was much stronger in the early 20th century. It's possible that could continue.

But Sen said the study, overall, shows political views can be fairly persistent. "Political attitudes are really sticky. They can actually persist from generation to generation," she told me. "My parents' political attitudes really influenced how I view politics now. And their parents' attitudes influenced how they view politics. And so on and so on."

The paper gives insight into why Republicans' Southern strategy works

The paper's findings aren't actually that surprising, because in some ways the political system has run under the assumption that something like this is already occurring.

Politicians have long used coded language — with phrases like "thug" and "superpredator" — to play up to white Americans' racial fears, particularly in the South.

Republicans in particular have homed in on this kind of language for their "Southern strategy" after the 1960s: By invoking many white Americans' racial resentment after the civil rights movement, Republican candidates took states in the South that had historically gone Democrat. (This amounted to a realignment: Democrats were once much more conservative on race issues — and, frankly, the party of racism — while Republicans — the party of Abraham Lincoln — were more progressive. But that changed after the 1960s.)

To this end, the study also found that the prevalence of slavery predicted Southern counties' support for Democrats when Democrats were the racially conservative party:

We've also long had data that suggests Republicans are more likely to hold racist attitudes. For example, Pew Research Center data from 2012 found 18 percent of Republicans disapproved of black and white people dating each other, compared with 5 percent of Democrats. And one study found that the Ku Klux Klan played a small but meaningful role in shifting Southerners' support to Republicans after the civil rights movement.

But Acharya, Blackwell, and Sen's study gives some explanation for why the Southern strategy can work: Republican candidates are tapping into not just contemporary race issues and concerns, but feelings that go back 150 years.

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