What can soil tell us about election results? After every election, analysts pore over piles of data in order to better understand political trends. But what if a better place to search for answers is the ground beneath our feet? More specifically, whether that soil was conducive to crops worked by slaves over 200 years ago? Listen to Maya Sen and Matthew Blackwell trace southern racial conservatism all the way back to glacial deposits.

Their new book, "Deep Roots," studies the swath of America where slave-based economies thrived as a result of nutrient-rich soil ideal for growing cotton. Hear them uncover the tangible legacy of slavery that continues to shape today's political life.

MAYA SEN: I think things like racialized rhetoric from the top down can have really, really damaging and long-term impacts. So things like talking about people in dehumanizing language, institutionalizing policies that treat people as less than human. Those things can really create attitudes that then persist for a long time.

Just even kind of looking back at American history, how could we not think that an institution that basically treated humans as less than human for 250 years, how could we think that that would not have a lasting effect two generations down the road? It's almost crazy to think the opposite, that it wouldn't have an effect.

CHRIS HAYES: Right.

MAYA SEN: I think the caution for Democratic theory, or Democratic governance, is how to avoid that moving forward. How can we avoid the missteps that we made historically? You see some of the missteps happening right now with things like forced separation of families and kind of this racialized rhetoric and dehumanizing rhetoric, and this is a dangerous path.

CHRIS HAYES: Hello, and welcome to “Why is this Happening?” with me, your host, Chris Hayes. Election night: it happened. It happened, it happened, it happened. I was in Texas, in El Paso. It was a fascinating night in Texas, which is, I think, one of the most interesting election night results for a whole bunch of reasons.

One of the things that happens after election night is those of us in the professional punditry business, we do a lot of slicing and dicing of what happened on election night. There's a bunch of different ways that you look at these results. You try to analyze what happened.

You look at where Democrats won and where they lost, right? That we saw that in some red states, like, for instance, Indiana and Missouri where both incumbent Democratic senators lost by fairly wide margins that the Republican coalition, is really strong in those states. Even with — In Missouri, Claire McCaskill was a very strong incumbent and a very canny politician unable to overcome the kind of tide pulling her out.

You look at Texas where Beto O'Rourke came within three points of Ted Cruz and a whole bunch of down ballot races went the Democrats' way, and you look at what's going on in Texas.

You look at things like candidate quality, right? Like, how good was the candidate? Beto O'Rourke, a pretty special candidate. Raised a lot of money. We analyze things like demographics, right? That's the first thing that people go to. You look at the exit polls, you look at what percentage of the electorate was under 30, what percentage of the electorate was Latino, what percentage of the electorate was over 65, right? There's all these different ways that we look at an election and we say, "What happened here? Why did this result happen?"

They tend to be about what's happening now, like, “What is the current composition of the demographics of a district or a state? What is the current education and income level? How much money did the respective candidates raise? How good was the candidate? What were the ads? Did Donald Trump visit? Did Barack Obama visit?” That's all the stuff that we put in the package of analysis when we try to figure out what happened in an election.

What if I told you this, what if I told you that a key determinant about what happens in a place's politics isn't the current demographics, current incumbent, or the current fundraising, but what was going on in that county in 1850?

What if I told you that the soil in the ground is a key determinant of the electoral outcomes in 2018? Because the soil in the ground, whether it was the kind of soil that you could grow cotton or tobacco in, tended to produce an economy based on slavery in the South that then produced a population mix of free white people and black slaves that then produced a cultural, political, legal hegemony that has endured for another 150 years.

What if I told you that you can go around to various countries throughout the South and you can compare the political outcomes today, which way they vote, between those counties that had a lot of slaves and those counties that didn't have a lot of slaves? What you will find is that that single fact about a county and about a place is wildly determinant of today's political outcomes.

That's kind of a crazy thing to think. It's a crazy thing to think, like, how can it be the case that something so long ago, so removed from the people living in the county now, and so removed from what ads are playing and whether Donald Trump visited and the white working class and all of this stuff, how can it be the case that this deep historical root is reaching out from the past like an arm coming out of the grave to snatch someone by the ankle and pull them back?

That is what the subject of today's podcast is about. It is a discussion with two authors who published a book that makes precisely that case. The book is called “Deep Roots: How Slavery Still Shapes Southern Politics.” It's by three people, Maya Sen, Matthew Blackwell, and Avidit Acharaya.

We had Maya Sen and Matthew Blackwell in studio. They are professors at Harvard University. And this book is one of the most mind-blowing books I've encountered recently. The book lays out an argument for the ways in which slavery – particularly the percentage of slaves in an area, right? Like, how much did slavery dominate a locality as a key determinant of all kinds of political and social and public opinion outcomes today in 2018 or 2016?

What's remarkable about the book isn't just the thesis, right? That's a – you hear that thesis and you think, "Whoa, well, that's pretty incredible." It is the reams of data and the rigor with which they have gone about setting out to show that this is the case.

A lot of people heard our conversation with Michael Tesler, who is a political scientist at U.C. Irvine, about race in the Obama and Trump era, and the data that he brought to bear showing all the ways in which race suffuses increasingly the political coalitions of American life post-Obama, the way that race and racial attitudes particularly have increasingly been sorting people into different camps.

I think of today's conversation as a kind of compliment to that because it's about the same theme. It's about how race sorts American political life, but it's in some ways even more profound. It's more profound as a way of thinking about the world because what Michael Tesler is talking about is racial attitudes today. People have racial attitudes, they change over time, and those racial attitudes are increasingly aligned with partisanship.

This is about the legacy – the very real, tangible legacy today – of an institution that was destroyed in 1865. It's so important to think about this because it is so constant in our discourse about the legacy of slavery or the Civil Rights Movement and Jim Crow.

I think there is this sense among a lot of people, not bad-intentioned people, not people with deep wellsprings of racial animus, that that was a long time ago and things have changed a lot. We had the Civil Rights Movement, and we have one person one vote, and Barack Obama became the president.

I think even people who don't subscribe to the overly simple thesis of, well, “Barack Obama was president, we conquered racism.” Like, put that aside. That I think is a pretty ridiculous view, but even thinking people, myself included, you think about the ways in which history sets the table for what we do today.

I think we all want to think of ourselves as people with agency and choices. We live in the now, and it's just really hard to get your mind around the level of historical power that this institution, slavery, had in American life, and particularly in the South where it endured for so many years.

Slavery's history is longer than America's history without slavery, right? So, just in sheer year terms, like, it was happening longer in the “new world” than the United States without slavery has been happening. America post-Jim Crow, which was essentially a means of attempting to restore the racial hierarchy of slavery without legal slavery, that's only been vanquished for 53 years, which is not a lot of time.

Today's conversation is a deep inquiry into what the historical record and the current record shows about the profound enduring power of slavery in today's American political life.

This is a great book. It's really convincing. It's pretty airtight, I think, actually. I found myself sort of skeptical in the beginning, and then persuaded by the end, which I guess is your job, right?

MAYA SEN: That's good. Yeah, I hope so.

CHRIS HAYES: You start with a question, a problem. What’s the problem you're trying to solve? What's the question you're trying to answer?

MAYA SEN: At its broadest level what we're thinking of is what makes the United States so conservative to other western democracies, right? [maybe it’s “compared to”?”] Because it is. We know the United States is more conservative on a host of social issues ranging from religion to gun rights to economic policy, but it's particularly conservative when it comes to racial attitudes. We actually started with that broad, broad, broad, broad question.

CHRIS HAYES: Can I ask the question how do you ... We know this, like, when you look at things like universal healthcare or you look at rates of redistribution and taxation across “OECD” countries, right? There's all of these ways in which the U.S. is more conservative, right?

MAYA SEN: Yeah. Yeah.

CHRIS HAYES: There's a bunch of stories you can tell about that institutionally, historical development, but when you're saying more conservative about racial attitudes how do you even measure that?

Counter protesters gather in Roxbury before marching to a planned 'Free Speech Rally' on Boston Common on Aug. 19, 2017 in Boston, Massachusetts. Thousands of demonstrators and counter-protesters are expected at Boston Common where the Boston Free Speech Rally is being held. Scott Eisen / Getty Images

MATTHEW BLACKWELL: There's a couple different ways we can kind of get into thinking about how to measure how racial attitudes. In particular, some of them are more direct. We just ask people, “How do you feel about white people? How do you feel about black people?” Whites in the South especially, but across the United States, tend to rate white people higher than they rate black people.

MAYA SEN: Yeah.

MATTHEW BLACKWELL: Just as a how warm do you feel towards people.

CHRIS HAYES: That's a thermometer…

MATTHEW BLACKWELL: We have things like that, but we also have more kind of subtle ways of getting at how conservative you are on issues related to race. Measures on policy attitudes that are related to race, things like affirmative action, policies that are seen to help particular minority groups, or these scales of racial resentment, which are a little bit more amorphous, a little bit more debated in political science literature, but that are trying to pick up when people are kind of not wanting to just reveal that they have socially unacceptable racial views, but they're willing to endorse statements that are in that direction.

These are the kind of measures that we're getting at in this book at least, and that political scientists have thought about, a lot about.

MAYA SEN: One other thing that's interesting about this is that I think that a lot of attitudes on policy also indirectly stem from attitudes on race, right?

CHRIS HAYES: Well, that's one of the theses, right? You look at the U.S., you compare it to other “OACD” [see previous note] liberal developed democracies. You see that it's more conservative in a bunch of ways. The question's why is that?

One of the answers, one of the places... This is a thing people said for a long time, is that race is this factor in American politics that have driven a more conservative sort of politics.

MAYA SEN: Exactly. If you look at the history of all of these countries there is one country that was really, really defined by slavery in terms of western developed democracies, and that is the United States.

Thinking about how we started getting interested in this, you have to start with that. That is one of the things that historically made the United States extremely distinctive. What other countries had a slave institution like the United States did? We're talking about Brazil, Caribbean countries. In no other western-developed democracy did you have an institution like this.

You have to think that it somehow left its mark on our institutions more formally, but also on sort of the content and character of the population.

CHRIS HAYES: If the question then becomes, okay, well, let's look at how slavery's impact and racial attitudes make the U.S. different, then you zoom in one more level on the Google map, right?

MAYA SEN: Yeah.

CHRIS HAYES: You start looking at a specific region of the country.

MAYA SEN: Yeah.

MATTHEW BLACKWELL: Yeah. We look at the South in particular because that's where the legal institution of slavery was around the longest. The North had some slavery, but it was mostly abandoned by the late or the middle part of the 19th century.

We try to focus on deconstructing this myth that there was a solid South, that views in the South were uniform across a host of racial attitudes, and try to show that actually there is a lot of variation in the South. It's a more heterogenous place than people might think, and a lot of that heterogeneity, a lot of that kind of variance is related to where slavery was in the middle of the 19th century.

MAYA SEN: One thing, too, is that I think people today forget just how prevalent the institution was in the South. Our data show this, the historical data show this – there were counties in the South where 90 percent of the population was enslaved.

You never saw that in the North. You never saw that outside of the South. It was sort of specific to certain areas of the South, and that's where we see kind of the strongest effects, but I think we sometimes forget just how prevalent the institution was and how concentrated it was.

CHRIS HAYES: Well, when you think about the solid South, right? You think about these maps, right? You look at maps of elections, when you look statewide it's almost always the case, right?

MAYA SEN: Yeah, it's just the blood red of the South.

CHRIS HAYES: Yeah, yeah. Or the blue when it's the solid blue before the red/blue markers are invented in the way they are. You think of it as this block, right? You think of the states of the old Confederacy. You look at electoral college map after electoral college map after electoral college map. What you guys do is you go down to the county level.

MAYA SEN: Yeah.

MATTHW BLACKWELL: Yeah.

CHRIS HAYES: There's a pretty wide variance at the county level.

MATTHEW BLACKWELL: Yeah. Well, it's a conservative place overall, but it's even within the conservatism there are areas that are just way more conservative than other areas. Some of this gets masked by – when you look at these electoral maps, even at the county level, they get masked a little bit by the racial diversity of the South, right? Obviously there are a lot of African Americans living in the South.

If you look at just a normal county-level map of the Obama voter share or the Trump voter share, or anything like that, what you'll see is a streak of blue in the areas where slavery was most prevalent. That's that demographic persistence where lots of African Americans live today and are voting for Democrats in very high numbers.

What that kind of masks is a lot of heterogeneity among whites that live in those same areas that are actually even more conservative than whites that are living in areas, say, upstate in different states that were... had relatively less slavery, was more yeoman farmers and things like that back in the 19th century.

CHRIS HAYES: Here's where you get to the ur-map of everything, right? When you do county by county maps of infant mortality, percentage incarceration, all kinds of things, they look really similar.

MAYA SEN: Yeah. Yeah. It's crazy.

CHRIS HAYES: Over and over again you keep seeing the same map.

MAYA SEN: Yeah.

CHRIS HAYES: You're like, "Oh, this isn't ... This is the incarceration rate map, not the infant morality rate map, but they kind of look like they fit right over each other."

MAYA SEN: You could put them one on top of the other and you could superimpose that with a map of slave prevalence in 1860 and you would see the exact same pattern. Then, you would put that on, on top of a map of cotton suitability and you would see the exactly same pattern again. Once you see it, it kind of pops out at you.

CHRIS HAYES: I mean, it's wild. Right. It starts with ... Let's start with what the black belt is.

MAYA SEN: Yeah.

CHRIS HAYES: Because that map is actually a map of a kind of soil.

MATT BLACKWELL: Yeah.

CHRIS HAYES: Is basically what that map is. The map that you see, that you can lay all atop each other, is a map of a certain kind of soil.

MAYA SEN: Yeah.

MATT BLACKWELL: The rich soil that was... There's the counties in the South, in South Carolina, called Richland. That's talking about the rich land. It was a rich soil that was very suitable for growing cotton, especially the kind of cotton that was being produced in the 19th century. That really expanded after the cotton gin was invented.

We saw this kind of wild progression westward from the coast where a lot of tobacco, rice, sugar was being planted. Kind of younger farmers were going west across this black belt, which cuts through South Carolina, Georgia, Alabama, Mississippi. That kind of ends at the Mississippi Delta, which is another huge cotton-growing region. All of these places were just really well suited for growing cotton.

CHRIS HAYES: The black belt refers to the kind of soil, right?

MATT BLACKWELL: Yes. Yeah, sorry.

MAYA SEN: Yeah.

CHRIS HAYES: Yeah. It's a geological phenomenon.

MAYA SEN: Yeah. I think it was caused by the glaciers receding.

CHRIS HAYES: Yeah, right.

MAYA SEN: They deposited all of this rich soil in this particular kind of hook-shaped region, and then along the Mississippi Delta when it floods and things like that.

CHRIS HAYES: So let’s take a step back because this is kind of a... This is, so, sort of almost philosophical question. It's insane to think about glacial deposits as determining electoral outcomes in 2018, but that's kind of an argument that's being made here.

Thousands of protesters prepare to march in Boston against a planned 'Free Speech Rally' just one week after the violent 'Unite the Right' rally in Virginia left one woman dead and dozens more injured on Aug. 19, 2017 in Boston. Spencer Platt / Getty Images

MAYA SEN: That's kind of an argument that's being made here.

CHRIS HAYES: Yeah.

MAYA SEN: Yeah.

CHRIS HAYES: Like, literally the glaciers receded here, and that receding led to this kind of soil, which led to slavery, which produces all the county commissioners being right-wing nuts.

MATT BLACKWELL: Yeah, so it is a little bit different than here's what typical political science is about, how big of an effect a mailer had on somebody.

MAYA SEN: Yeah.

MATT BLACKWELL: These are really long-term things. I think it's not surprising that these huge monumental things have a massive effect on politics today. It's just... Part of the challenge for the book for us was to just try to figure out –

CHRIS HAYES: Tease that out.

MATT BLACKWELL: Yeah, exactly.

MAYA SEN: Yeah. When you think about it, it makes sense, right? Because the type of soil structured the type of society that grew up in those places.

MATT BLACKWELL: Exactly.

MAYA SEN: The type of society that grew up in those places was heavily, heavily reliant on a very solid racial hierarchy. It required inexpensive black labor to till this fertile land. That set the stage for what we talk about in the book and sort of the development of racial attitudes.

It sounds crazy to step back and kind of think of the nature of the soil kind of dictating all of the next 250 years, but it really did structure how a society was organized when those places were settled.

CHRIS HAYES: That's because at this expansion point after the gin, right, when cotton is king ...

MAYA SEN: Yeah.

CHRIS HAYES: There's just unbelievable insatiable... That region is the – Is to cotton what Saudi Arabia is to oil.

MAYA SEN: Yeah.

MATT BLACKWELL: Yeah.

CHRIS HAYES: It's the place. 200 years from now I'm sure the way that they take the oil out of the ground in Saudi Arabia will continue to structure Saudi politics.

MAYA SEN: Yeah, yeah. Exactly.

MATT BLACKWELL: Yeah. Yeah.

CHRIS HAYES: That produces the slave society of the South along the black belt, but not everywhere. That's the key point.

MAYA SEN: Not everywhere.

MATT BLACKWELL: Yeah.

CHRIS HAYES: Right?

MATT BLACKWELL: Yeah.

CHRIS HAYES: If you go and you've got this comparison of Greenwood, Mississippi, which is in the heart of the black belt, and Asheville, North Carolina, talk to me about the difference between those two places.

MAYA SEN: Well, a place like Asheville, it's more mountainous, it's cooler. It doesn't have the kind of climate that you need for large-scale cultivation. That's what really predicts the rise of the slave society. Was the ground and was the soil suitable for growing tobacco, rice, indigo, or cotton?

If that's the case then you then saw a prevalence of slavery kind of rise up. Places like Asheville, other places kind of up in the Upland counties in the South, Appalachia, places like that that were not suitable for that, they never had this kind of prevalence of slavery. Because of that, they never had this kind of rigid racial hierarchy kind of rise up.

Places like that are actually, according to our data, more liberal. They're not as liberal as places in the North, but they are much more liberal than places in the deep South. I'm talking specifically here about the attitudes of whites.

CHRIS HAYES: Attitudes of whites, yeah.

MAYA SEN: Yeah, which is a really important point in all of this.

CHRIS HAYES: Yeah. Right.

MAYA SEN: Yeah.

CHRIS HAYES: You're controlling here. The apples to apples comparison is white political attitudes in a place like Greenwood, Mississippi versus a place like Asheville.

MATT BLACKWELL: Yeah.

MAYA SEN: Yeah. Yeah, because ...

MATT BLACKWELL: That's right, yeah.

MAYA SEN: On paper, they actually vote for Obama, just to give an example, at roughly the same rate, but Green –

CHRIS HAYES: Oh, that's interesting, so you can't find it in election returns.

MAYA SEN: You can't find it in election returns. In fact, when you look at the black belt, the black belt, that's where Obama had some of his greatest support outside of metropolitan areas. We tend to forget sometimes I think…

CHRIS HAYES: But that's among black voters, just to be clear.

MATT BLACKWELL: Yeah.

MAYA SEN: Yeah, it's among black voters. We tend to forget rural black voters.

CHRIS HAYES: Right.

MAYA SEN: We tend to... When we think of rural voters I think oftentimes the narrative is about white voters, but in the South there are a lot of rural black communities. A lot of them actually kind of stayed on after the collapse of slavery and moved to other cities in the black belt, but stayed in the area. These are parts of the country that are still heavily, heavily African-American, which is really interesting.

MATTHEW BLACKWELL: On the state level you can kind of see this with a place like West Virginia. West Virginia was part of Virginia before the Civil War, and it did have legal slavery. It didn't have very much slavery, and we tend to think of it as a very conservative place, but actually, when you look at the white people there, they're actually a little bit more liberal than some of the white people in the deepest part of the Black Belt. It's hard to see that from the politics 'cause you look at the maps and it just looks like a solid, solid red.

You look at Georgia and well, there's a lot of blue in Georgia. Georgia looks competitive. And West Virginia's never competitive. But if you actually just, again, look at the white people, just the apples to apples comparison like you were saying, the people in West Virginia are actually relatively liberal. They've gone back and forth in terms of electing different types of partisans and things like that over the course... They were the only place to kind of have Republicans, back when it used to be a totally Democratic south.

CHRIS HAYES: Well they broke with the state of Virginia over precisely the fault line we're identifying.

MATT BLACKWELL: Yes, exactly. Yes, yes.

CHRIS HAYES: And because they, again, they didn't have the good soil for the cotton. So they didn't have slavery, and so they broke the state apart over the Civil War.

MATT BLACKWELL: That's right.

CHRIS HAYES: So what you're saying, we think about West Virginia in contemporary parlance as like, the heart of conservatism at some level. And you're saying that when you zoom in and you look at white peoples' racial attitudes, or their... Is it racial attitudes? Or their broader conservatism?

MAYA SEN: That's a good question.

MATT BLACKWELL: In the book, what we look at is a host of different measures. And what we find is that we find effects on things like partisanship. White people in higher-slave areas, they tend to be more likely to identify with the Republican party. They tend to be more likely to oppose affirmative action. They have cooler feelings toward African Americans. They have these higher levels of racial resentment that I mentioned earlier. And so what we don't find strong effects for are kind of issues that we think are unrelated to race. Things like support for environmental policies. Support for military interventions.

MAYA SEN: Reproductive rights issues.

MATT BLACKWELL: Yeah. Abortion and gay marriage, for instance. Those are not issues that we see big effects on.

CHRIS HAYES: But things like policing and crime and also, crucially, redistribution, right?

MAYA SEN: Exactly.

MATT BLACKWELL: Yeah, redistribution is a big one, yeah.

CHRIS HAYES: Redistribution's the big one where, is the Venn diagram overlap in terms of the racial conservatism and more broadly conservatism.

MAYA SEN: Yeah, exactly. And there's been a lot of work in political science documenting that. But I think it's really important also to point out that in the South, partisanship and racial identity are, historically, intimately intertwined. If you were white you supported the Democratic party. If you were black you almost certainly supported the Republican party, historically, right? And this changes in the 1960s and things get more complicated, but it's certainly the case that partisanship was intimately intertwined with the racial messages being sent by the parties, and also the racial identity of the voters.

CHRIS HAYES: So one thing you capture is that there's variance at the time. So let's talk about that, right? So when you think about the Confederacy, you think of them as a fairly united entity. And one of the things I think that's fascinating, as I've gotten more into Civil War history, just discovering that there were Southern Unionists. There were Southern whites who had – not a lot of them – but actually had some pretty decent ideas about race. They were fairly rare. But you have these graphs, like you look at the votes of legislators in Georgia, from the places that have lots of slaves and places that don't, and they diverge in 1860.

MATT BLACKWELL: Before the Civil War. In the lead-up up to 1850, up to 1855, we actually see that these areas look largely similar. And that's because of these two, at the broad level.

MAYA SEN: In terms of how they voted.

MATTHEW BLACKWELL: How they voted on all of these things.

MAYA SEN: Political issues.

MATTHEW BLACKWELL: Political issues, on things like expanding the slave trade at various points. We see that there's broad agreement that slavery is a good institution. That we should continue as part of the South. Now what we find is that right at the time of the Civil War, when it becomes clear that there's no longer gonna be this institution, or it's not gonna really last that much longer, the appeal for the places that didn't have it at the time also becomes a lot less. So we see big divergence emerge there.

MAYA SEN: There's an interesting analogy in the historical period to home ownership. I know this sounds crazy, but I think a lot of people, a lot of whites in this historical period in the South, viewed owning slaves as a step forward in terms of accumulating wealth. It was like owning a house back then. You know how you're told, "Save up for your down payment, and once you buy a house you'll be on secure financial footing and you'll have a legacy to leave to your children," things like that. That's sort of how people viewed – people in the South, white people in the South – viewed slave ownership. They viewed it as a path toward building wealth, toward financial security, and all of a sudden in the 1860s the message was like, "Holy cow, that institution is not gonna be there anymore. Why the heck am I supporting that other guy who got in early and was able to make a fortune off of that wealth. Why am I still supporting that guy?"

And so there's this huge kind of divergence at that point, in part because the institution is clearly starting to collapse and so it's no longer this viable path forward for people who didn't already have it. So I think that's sort of an interesting way to think about it from our contemporary perspective, I think that's how people viewed it. It was a path for wealth.

MATT BLACKWELL: So there were some, again, not a lot, but there were some poorer farmers that said, "I don't really want to fight this rich man's war." You know, to basically protect the property, so to speak, of these rich landowners. So you start to see some of that emerging right at the time of the Civil War.

CHRIS HAYES: You start to identify the divergence there, right? And the kind of argument of the book is that the prevalence of slavery in counties back then is predictive of racial attitudes now?

MAYA SEN: Yeah.

CHRIS HAYES: And political culture now.

MAYA SEN: Yeah. And also other things historically. That's the thing, it doesn't sort of appear now, we can actually very carefully trace out the exact kind of path forward that these attitudes took. So we can show that slavery in 1860 predicts where there were lynchings in the time period around the 1920s, when there were a lot of lynchings happening. We can show that it's related to kind of differences in educational outcomes before the passage of the Civil Rights Act in 1964 –

CHRIS HAYES: Wow.

MAYA SEN: – various components of income inequality and redistribution in the New Deal era.

CHRIS HAYES: So racial violence and racial terrorism, racial inequality in schooling, racial inequality in income – you can all predict them based on the prevalence of slavery as an institution and slaves as people back before the Civil War.

MAYA SEN: Exactly.

MATT BLACKWELL: And we see it in presidential elections too. Back then the Southern Democrats were really strong, and so we see massive differences in terms of voting for Republicans between the low slave and high slave South at this time. That it kind of peaks around the 1920s. And then as time goes on, we see that kind of declining a little bit but really not declining all that much. The effect that we detect today in terms of the politics is roughly similar to the effect that we saw in terms of its magnitude on say the George Wallace vote in the 1960s or something like that.

CHRIS HAYES: You're saying the effect is as strong now as it was in 1968.

MATT BLACKWELL: Certainly for the... For Barack Obama's, Barack Obama –

MAYA SEN: Yeah, Barack Obama was… Talk about someone who activates racial resentment. I mean, that is something where you can see it very clearly kind of jump out is the slavery's effect on Obama vote share.

CHRIS HAYES: Slavery's effect on the Obama vote share.

MAYA SEN: Yeah, yeah.

Protesters block both directions of Interstate 580 in Oakland, California, on Aug. 12, during a rally against racism in response to the violent clashes in Charlottesville. Josh Edelson / AFP - Getty Images

CHRIS HAYES: We've got an independent variable in the prevalence of slavery in counties. We've got a whole host of dependent variables that you just listed. Those dependent variables are Obama vote share, income inequality, racial education gaps, prevalence of lynching, all sorts of outcomes of racial politics, right?

MAYA SEN: Right.

CHRIS HAYES: You're trying to convince me, right? That this thing, this independent variable has a causal relationship to all these dependent variables. And now you gotta convince me that this isn't just some correlation, there's not some other driving causal factor in the background because it's a tough pill to swallow to tell me that the receding glaciers and the soil that they created and the institution of slavery is like telling me who's voting for Barack Obama. 'Cause we're all autonomous human agents who sit thinking like, "Well, who I want to vote for, oh who are you voting for?" And you're saying, 'No, it's just in the soil, dude."

MAYA SEN: I'm gonna let Matt answer this because he's the expert on causality but I think ... So this is a very common reaction we've gotten is, "You're telling me that you can tell me who I'm gonna vote for based on my family history and where I'm from." The answer is I think we really underestimate the extent to which our politics is informed by the politics of our families, our parents and our communities. I mean, I just think in general we kind of underestimate –

CHRIS HAYES: No, because we like to tell ourselves we're sovereign over our own minds and souls.

MAYA SEN: I mean, that may very well be true but our politics are generally the politics of our parents, right? We know this, we know that-

CHRIS HAYES: Is that true in the literature? Is that establishes?

MAYA SEN: It's true.

MATT BLACKWELL: It's a pretty high correlation.

MAYA SEN: It's true, there's a really high correlation. It's not one to one but it's like point nine five or something. So I mean, you can tell a lot about my politics based on the politics of my parents.

MATT BLACKWELL: The big way that we're approaching it is to think about using ... Leveraging the fact that there's this kind of, that nature gave us kind of an experiment. In some places it put good soil for cotton and in other places it put kind of not so good soil for cotton –

MAYA SEN: But like a mountain or like rocks –

MATT BLACKWELL: We'll put a mountain there, or it's in the wrong place and so we're gonna kind of leverage that kind of variation, that's kind of like to recover the hidden experiment that exists in this data to allow us to assess, “Okay, how do we get the causal effect, it's not due to something even more ancient.” So we do that in the book and we try to be very careful about it. I think –

CHRIS HAYES: And partly because one of the things about the slave empire is that there is a lot of data. That's part of it, you're dealing with lots of data. You can say, “This county had records.”

MATT BLACKWELL: Yeah.

CHRIS HAYES: Right? You've got the data.

MAYA SEN: Yeah.

MATT BLACKWELL: We leverage any data we can get, so we were getting census records. We were getting... going through and actually looking at census sheets from “Ancestry.com” to get at mortality rates for slaves and for non-slaves.

MAYA SEN: We also pulled down terrain data and soil quality data from the United Nations to try to figure out what parts of the South were particularly good for growing cotton, tobacco, rice, things like that. I mean, that's like, talk about kind of engaging big data, right? Because we're looking at historical data but we're also looking at contemporary data, but we linked all of this together and try to kind of explore precisely this fact. And it turns out that the early settlers from this part, they actually knew what they were doing. They gravitated toward those parts of the South that were particularly good for growing these crops.

They weren't dummies. So it turns out there's a strong relationship between how suitable for growing cotton a place is and the prevalence of slavery around this time period. There's one interesting exception, which is Florida. Florida is actually pretty good for growing cotton but it turns out it had a really, really high Native American population that was sort of intractable for –

MATT BLACKWELL: And it was only accessible to Southerners after 1830 or so –

CHRIS HAYES: Right, it's a pestilential swamp.

MATT BLACKWELL: Exactly.

MAYA SEN: Yes, I didn't want to say that but –

CHRIS HAYES: The problem with Florida is that –

MAYA SEN: It presented challenges.

CHRIS HAYES: No one should be living there and yet here we are.

MAYA SEN: Yeah, so apparently it's good for growing... Certain parts of the state are good for growing cotton, but yet you didn't see that economy develop for other reasons. That's sort of the one exception.

CHRIS HAYES: So you've got all that data that allows you to sort of try to look at this, what you're calling a natural experiment, right? And then how do you make the case that there's not something else happening that's driving these outcomes, that's coincident with this?

MATT BLACKWELL: Yeah. So I think the big one that we tackled in the book and we think about are what about all the African Americans that live in these areas now. And couldn't it just be that the whites that are living in the highest slave areas now are interacting with African Americans today and it has nothing to do with the legacy of slavery that's going through their family history and all these attitudes that are persisting over time. And so we spend a long time in the book thinking about –

MAYA SEN: It's the contemporaneous interactions that they have with African Americans that makes them more racially hostile.

CHRIS HAYES: Which a lot people talk about it terms of racial threat, right?

MAYA SEN: Yeah, that's exactly –

CHRIS HAYES: The thesis is, it's not this sort of hold over historical, what you guys call, I think “behavioral path dependence” in the book, it's instead, people get conservative when they're under threat, this is something that we know from literature and all sorts of environments. They are living in areas that have high percentages of African Americans. And so they're conservative and racially conservative and want to keep their piece of the pie away from the threatening group that's near them.

MAYA SEN: Yeah.

MATT BLACKWELL: Yeah, that's right. The simplest way to think about it is if you were to look at counties now that had similar levels of African Americans, but had differential levels of slavery in 1860, you still see this kind of effect.

MAYA SEN: Of slavery.

MATT BLACKWELL: Of slavery. So you still see a big difference in terms of racial attitudes. Even if they have the same population levels of African-Americans.

CHRIS HAYES: It cannot just be the case that if you're a small group of, a relatively small group of white Southerners, living in an area with a lot of African Americans, and you think to yourself, “Man, they’re gonna vote us out of hearth and home,” whatever crazy conservative fantasy you have. That when you match those two sort of things, you still are seeing this sort of effect from the prevalence of slavery.

MAYA SEN: Exactly.

MATT BLACKWELL: Yeah. And in fact, we also showed –

CHRIS HAYES: It's wild.

MATT BLACKWELL: It is –

CHRIS HAYES: That's a wild finding.

MATT BLACKWELL: It is, I mean, the other thing that's true actually in the South is that it kind of runs... All of the kind of basic correlations run counter to what you'd expect from racial threat. The whites that actually live closest to African Americans are the most liberal in the South. The areas of the South that now have the highest levels of African Americans are actually –

MAYA SEN: There's a lot of cities too.

MATT BLACKWELL: Some of it's cities but even if you drop cities, you see this effect where whites that live in the same say zip code as lot of African Americans tend to be more liberal.

CHRIS HAYES: That's fascinating.

MATT BLACKWELL: Yeah.

CHRIS HAYES: So that's literally the opposite of what you would predict from the racial threat. My thinking about this is always informed by the fact that… in reading particularly reconstruction literature and thinking about the apartheid state of South Africa, right? Which is, like, the most intense version of this. A small white population under a rigid, murderous hierarchy, in which they know they're outnumbered. And that's true in South Carolina, it's true in Mississippi.

MAYA SEN: Mm-hmm.

CHRIS HAYES: Those are the two states. And when you look at those states, those have the most, arguably the most reactionary politics across the entire South, particularly around that time and particularly when you look at the redemption that happens. It's the most violent, the most brutal, the most murderous and the most hateful in the positions in which there's this fear of being outnumbered.

MATT BLACKWELL: One thing that is true is that, while we don't see the kind of levels of African Americans, it doesn't really help us predict too well conservatism in the South. What is true is that we do find both historically say, reconstruction and contemporarily, that you see kind of changes. If there's a big change to the society at any given time, or the size of the population, that can trigger some of these threats. But it's not just living near a group of people that you've lived near your whole life, it seems like. It's about something changing in the environment that's kind of leading to these kinds of reactions.

And it's consistent with what we see in, again, in reconstruction, where there was a massive change to the legal environment and the social environment, economic environment, that lead to a good deal of reaction from the whites, especially in the areas where there was slavery.

CHRIS HAYES: So you're making this causal case, let's rule out the sort of demographic threat thesis and say, okay, I buy you that this is the causal mechanism. Then you gotta say like, what is that? I wake up every morning and I'm a white guy in Greenwood, Mississippi and I drive to my job and then I drive home and I watch TV and whatever. I'm going about my life. Why does it matter? How does it get in my brain? What's doing it?

MAYA SEN: So I think it was already in your brain, so wasn't that it was sort of delivered there at any one moment, it's that you grew up with an ambient environment in which race was sort of an intricate and an important part of your upbringing and your education. So I think we tend to forget kind of this history but the Civil Rights Act was passed in 1964 – not that long ago, and in response a lot of communities in this part of the country actually just shut down their public schools or the white students all shifted enrollment to segregation academies.

So in Greenwood, Mississippi, which is one of the cities that we profile in the book, I believe the lion's share of white students attend a private academy –

CHRIS HAYES: That's like a segregation academy.

MAYA SEN: Yeah, that started out as a segregation academy. It's not so much that you wake up one day and sort of realize that you're in this kind of racial hierarchy – it's an entire part of your being. It's filling the ambient environment that you grew up in and the way that you were raised. I mean, I think it's hard for us to kind of understand that, but I think it runs pretty deep and it's reinforced by the types of schools that whites were attending. Family structures, all different kinds of socialization. And that's just in the contemporary period, right? So we go back one generation, then we talk about actually kids going to lynchings. This is not that far off in terms of –

CHRIS HAYES: Right, one generation back.

MAYA SEN: About one generation, yeah. We talk about this in the book but there were some really, really high profile lynchings in the 1930s. At that point there were journalists who were taking pictures or other people were taking pictures and you can actually see in the pictures, young children. So this is in the mid-1930s. Those children today would be in their 80s. It's very likely that some of those children are still alive, they're still voting, 'cause we know older people vote more. They're still politically active and participating in politics and more importantly, they had children, they had families, they probably grew up sort of telling these stories and kind of raising their kids in this kind of culture that hasn't really dissipated yet.

MATT BLACKWELL: There's an amazing kind of work in sociology tracing out this idea of racial etiquette in the South and how young people were raised from – young white people and young black people –were raised to just be constantly thinking about race. How to interact with members of the opposite race. When deference should be given when you're walking around, what are the rules about talking, about different kinds of greetings and things like that. What you could and couldn't say to people and it's structured, especially in the early part of the 20th century, it's structured life in these areas.

CHRIS HAYES: Yeah, I think part of what modern day audiences have a hard time with is – if you read Solzhenitsyn or if you read “Vaclav Havel” or other people who were in Soviet sphere influence and totalitarian societies, right? – there's this kind of airless quality, in which, it's a totalitarian society, that's what the word means. It's all encompassing in the guidance of everything. It's like the slave society was that. Slave society was a totalitarian society. Like, everything. It was everything. It wasn't like there was this institution over there – that's like a thing, like, “We really like soccer around these parts.” It was totalitarian, the entirety of social, political, economic relationships were embedded in, revolved around, theorized and justified the institution.

MAYA SEN: Right and not only that, but the strength to which that happened was varied and was the greatest in these parts of the South.

CHRIS HAYES: Right, exactly.

MAYA SEN: And places where it was like 90 percent slave, that was how you lived, you breathed, you ate. It was all around you and it structured every kind of interaction that you could possibly think of.

MATT BLACKWELL: And to some extent after slavery ended, some of the locality, the kind of specific local areas became even more important. There was no kind of laws that were necessarily gonna encompass everything. Be able to kind of preserve the same structure, economic structure that we had –

MAYA SEN: We tried.

MATT BLACKWELL: We had with slavery but it required a lot more kind of local vigilance to kind of enact these policies. So you had a kind of creation of a culture, a maintenance of a culture that required things like extrajudicial violence, it required basically training and indoctrinating young children into thinking about the world in certain ways. Whereas, I think in the antebellum period, they didn't need as much of that indoctrination because it was just the way life was. In fact, one interesting thing about the South is you see a lot more contact – interracial contact – before the end of slavery because there's a legal structure in place to kind of control it. Afterward, there's no legal structure, rights are up for grabs, and now we need to actually put in place some rules about this to make sure everyone knows their place. Because legally now everyone has to.

CHRIS HAYES: There's like a militancy that comes in the wake of reconstruction.

MAYA SEN: Exactly.

CHRIS HAYES: Because now local authorities – particularly when the federal troops leave in 1877 – the local authorities are now going to be the ones that enforce the slave hierarchy that had been sort of ubiquitous and legally enforced beforehand, and now it's, like, it's going to be the town sheriff of Greenville, Mississippi who's going to make sure the people are in their place using whatever means he has at his disposal.

MAYA SEN: Yeah, but it's also families. Families were enforcing it. Parents were enforcing it, right? Because before, in the Antebellum period it wasn't as threatening, right, because you had the sanction of the law in place so that everyone knew where they belonged. And slaves are so devoid of any rights, that to use language of racial threat, it wasn't threatening. But all of a sudden they did, and so there was just a readjustment that had to happen in terms of how social norms operated that reminded both whites and blacks of what their respective place was.

CHRIS HAYES: Well, they could have just accepted equality. It didn't have to happen. To reimpose the murderous tyranny of racial hierarchy and hatred...

MAYA SEN: Well, yeah. And this is something we talk about in the book. We use this language from the political science literature in comparative politics. It's called “critical junctures,” right? So the South had this critical juncture. They could have gone down the path of racial equality. It was forced on them, but now that they were in that position, they could have chosen to go down that path.

CHRIS HAYES: And some parts did. They desegregated the street cars in New Orleans, Louisiana. There were some relatively liberal regimes around racial politics in port cities like Charleston, even. There were places where that did happen.

MAYA SEN: There were places, yeah. And then with the withdrawal of federal troops, you had different political interests in place that actually stepped back from that and moved in a different direction, which is retrenchment, reestablishing a racial hierarchy to the extent that it could be established through social norms and local ordinances and “black codes” and things like that.

CHRIS HAYES: And then just pushed generation to generation to generation.

MATT BLACKWELL: Yeah. I mean, and some of this also comes from the economic structures that were still lingering, right?

MAYA SEN: Yes.

CHRIS HAYES: Right.

MATT BLACKWELL: Even after the end of the Civil War, they still either wanted to or felt they needed to produce cotton.

CHRIS HAYES: They don't redistribute the land by and large.

MATT BLACKWELL: No, that's right. So we still have...

CHRIS HAYES: Thaddeus Stevens was right about that.

MATT BLACKWELL: Right, yeah.

CHRIS HAYES: They should have taken every goddam last acre.

MATT BLACKWELL: So even if it wasn't the exact same land owners, it was still white – it was largely white land owners that had big lots that were still trying to figure out, “How do I... Before, I was making this with essentially free labor, in the sense of how much you paid for it, the marginal cost of a labor, and now I have to pay for that on a wage basis, and how did I make that work economically?”

Some of the reasons for the racial structures were economic – “We want to make sure that it's the case that we can get the cheapest possible labor in this new legal regime.” And one person that we read a lot for this book and was inspired a lot was DuBois, who really saw a lot of this stuff very clearly at the time. And you see a lot of the structure being put on this that kind of preserves the attitudes that we're looking at, are being put on there because of the economic drives for the white landowners at the times.

And as that starts to fade with mechanization – So all of a sudden, cotton starts be able to produce at cheaper labor rates without as many people, you start to see a weakening of this a little bit. And that's where, the middle part of the 20th century, that's when things start to decline. And we find that the places that had declined the earliest, that had mechanization in earlier times, we see a little bit of this relationship for those areas.

CHRIS HAYES: What's crazy, too, right, is that part of what makes the endurance of this effect last is that the places that were high slave counties are not places a lot of people are moving to, a lot of white people are moving to.

MATT BLACKWELL: The thing that's maybe not surprising about internal migration in the United States, at least the way we can find it, looking at... It's hard to study. We don't have a lot of data on it, but the times that we can get data, what we find largely are the people that move, they largely move very locally, actually. Most moves are within county. The next biggest set of moves are to the next county. And by and large, if there is a move, people are moving from, say, a low-slave county to a low-slave county, or from a high-slave county to a high-slave county.

CHRIS HAYES: Fascinating.

MATT BLACKWELL: So you really see a lot of migration within these kind of bubbles, maybe so to speak, but you don't see a lot of migration in or out.

MAYA SEN: This is within the South.

MATT BLACKWELL: This is within the South. But even if you think about the people that are moving into places like Asheville and Atlanta, they're moving from low-slave areas, like presumably, the North, the West, the Midwest, into the low-slave areas of the South. You see a lot of this within, but not a lot in between.

MAYA SEN: I think, more broadly – I think the fact that you can still see the effects of slavery in 2018, despite the fact that there's a lot of migration in the United States, is a testament to how strong this legacy is, right? So we still see it, even though there's been all this migration.

CHRIS HAYES: Is there anything comparable?

MAYA SEN: Historically?

CHRIS HAYES: Yeah. It's famously called “the peculiar institution.” There's just nothing like it. There's no other analog. There's no institution... I mean, it's why those maps look that way, right? It's like there's nothing that happens anywhere in the country that is as totalizing, as enduring, and as central as slavery is in the U.S.

MAYA SEN: I think in terms of U.S. history, I think you'd have to look at something as basic as the Constitution or state boundaries to think about things that have structured our behavior and our attitudes in such a significant way. There are other institutions that have had a similar imprint on people's attitudes that have a very specific context.

So for example, there's really great research showing the lasting effects of the African slave trade on the attitudes of Africans today. So there's some interesting research on that. There's some interesting research on German partition. A really, really old example, there's some interesting showing that anti-Jewish pogroms around the time of the black death can actually still predict contemporary attitudes in certain parts of Eastern Europe.

CHRIS HAYES: Wow. That's going way back. Wow, that's crazy.

MATT BLACKWELL: And going even further back, the countries that had the plow for their agriculture, today have the views on women's roles in the house and the female labor force participations are very different. So places that had the plow...

CHRIS HAYES: Wait, really?

MAYA SEN: Yeah.

MATT BLACKWELL: Yeah, like 3,000 years ago, are more likely to have lower labor force participation by women because the plow kind of set up the family structure...

CHRIS HAYES: Specialization.

MATT BLACKWELL: Yeah, specialization in the home.

CHRIS HAYES: So you get the plow and then because the plow is a big thing, then you specialize inside the home, you get the bigger person to wield the plow, and then you create a family institution that's centered around that specialization but that endures to female labor participation rates.

MATT BLACKWELL: Yeah, and some political outcomes as well for women in legislatures and things like that. So part of the reason we got inspired to write this book is because we were seeing this in a lot of different contexts. There are these massive institutions that had huge impacts on societies, not just the U.S., but other contexts as well. And it just seemed like in academia we tend to focus on little things, the little small things that happen and...

MAYA SEN: Did you get a mailer? Did someone call you?

MATT BLACKWELL: Yeah, exactly. Did rain affect your turnout or something like that? Those are important questions that we should really...

CHRIS HAYES: That is some high-grade poli-sci shade. You guys are going to be real big hits at the next conference.

MATT BLACKWELL: Yeah, but I think it makes sense though that there would be these bigger, these huge institutions that shape fundamentally how society is formed.

CHRIS HAYES: What does it mean for politics today? How long is this going to endure?

MAYA SEN: I think it's really important to say, for people who haven't had a chance to read the book, that there are actually a lot of things that have happened in the interim that have made things better. So I think a lot of people come away with, "Oh, this is a very pessimistic story. It's going to last indefinitely. These differences are going to last forever and ever."

And the truth is that federal interventions have been really effective at addressing behavioral outcomes – so differences in education levels, differences in income levels, the rights of African-Americans, the ability of African Americans to vote. Those things have been really, really effectively addressed by the Civil Rights Act and the Voting Rights Act and other kinds of federal interventions.

So discriminatory behaviors can be addressed. I think it's just really important to get that out there. What's really much harder to address are people's attitudes. That's where it does seem like there's a very strong persistence. Attitudes are really hard to change. You can't pass a law that changes someone's attitude. It has to come from grassroots, ground-up change that really changes the cultural and social structure of a place. And that's much harder to do with any kind of legislation. It is going to change. It's just going to take a long, long time. How long? I don't know.

MATT BLACKWELL: And it's not clear. Some people think about this like a day.

CHRIS HAYES: We got 12 years before the world melts anyway.

MAYA SEN: Yeah, it's not going to change...

CHRIS HAYES: So I think we'll probably just kind of keep it. The errors of the slave legacy just will run right into the climate catastrophe era and just sort of abut each other in a nice way, so I think that will be probably be pretty good.

MATT BLACKWELL: Yeah, it's also, it's somewhat hopeful. It's not clear that necessarily these have to go in the direction of what you might call “progress,” in the direction of becoming similar, more similar, and more similar. Or it could be the case that you could have things that change. Like say, if these federal interventions like the Voting Rights Act were so effective, it's not clear that if you take them away, if you get rid of some of those protections from the Voting Rights Act, if those attitudes are still there, you could see things get worse.

MAYA SEN: Yeah, which is kind of what we're seeing right now.

CHRIS HAYES: One thing that I think about in these terms is, to go back to your point about the most amount of cross-racial interaction, actually you have more liberal racial attitudes among whites. And we know that in the immigration... there's immigration literature on this, right? That people's attitudes towards immigration are the most liberal when they're just around a lot of immigrants, which, to me, is always a hopeful story, right, because you can structure society to produce more immigration and more people being around each other.

And the hopeful version of that is that you can pass laws, you can do things around a million different things that have to do with zoning and schooling and transportation and job opportunities and things like that that use policy to integrate a society and that an integrated society actually can product attitudinal changes.

MAYA SEN: And I think an important point that I think is related to that is that there's no question that people's attitudes have attenuated over time and softened and even the language that people use to talk about people of a different race is now different than it was pre-1960. People were very comfortable expressing a certain kind of racism and very racially hostile attitudes in a way that just doesn't happen anymore, and we can really attribute that to cultural changes that have happened since, like the Civil Rights Act, greater integration and things like that. So I think it is important to say we have a hard time quantifying that, because it's a hard thing to think about, but...

MATT BLACKWELL: Yeah, you might say that the level of hostility has maybe shifted, but the alignment of where the places that are more hostile and less hostile, that has basically stayed the same.

CHRIS HAYES: Right, right, right. The differential, as opposed to the absolute level.

MATT BLACKWELL: Right, exactly.

MAYA SEN: And we also have to think, I think, in the age of Trump... We wrote this book in the last two years of the Obama administration, so it's hard to think about how things have changed.

CHRIS HAYES: Well, things are basically the same.

MATT BLACKWELL: Yeah, basically.

CHRIS HAYES: Yeah, pretty much.

MAYA SEN: I think maybe what we're seeing now is more freedom to express views that were longstanding. So maybe we thought that things were getting... that the discourse was improving, maybe more so than it actually has, and now we're kind of seeing people's maybe truer attitudes.

CHRIS HAYES: I mean, the combination of those two things, right? The idea that, well there's sort of etiquette changes, right?

MAYA SEN: Yeah.

CHRIS HAYES: There's "political correctness," or whatever changes to the taboos of language. The attitudes are still there, and then you get license to go back to the old taboo language, because the attitudes are still there, because of precisely the endurance effects that you're describing in the book. It's like, "Okay, well now I can say that."

MAYA SEN: When the Charlottesville protest happened, it's something that we would exactly predicted with our book. Right, the location, what it was about, the Confederate statues, kind of this turmoil about statues that were put up in the 1920s and 1930s. I mean, these were not even put up during the time of the Civil War.

They were put up actually in the exact time period that we talk about in the book as being particularly important for these political and racial cleavages. So even something like that, that you would not have seen during the Obama era, the Charlottesville protest, are predicted by the forces that we talk about in the book.

CHRIS HAYES: What does it say about democracy as an enterprise that these enduring, predictive effects exist? You're telling me that it's like, everyone's running around, right? And there's some sense in their head in democratic theory that we are citizens who are evaluating through the process of public reason, arguments about what we want to do, and you're saying that, “No, just look at the county and I'm going to tell you how the white people are going to vote.” And it's like, that does some deep kind of damage to the most elevated – or one might even say naïve – version of Democratic self-representation.

MAYA SEN: I mean, nothing that we say discounts the fact that you can steer away from your own socialization and your own family history. And we actually have encountered a lot of narratives of people who grew up in the deep Southern areas and actually grew up in this culture, whites, and who've actually stepped back away from it and actually have had the opportunity to reflect about it and how all-encompassing it was and have really come to change their attitudes. I think maybe we have more lessons about moving forward.

CHRIS HAYES: The legitimacy of Democracy is like an actual expression of any...

MAYA SEN: I think things like racialized rhetoric from the top down can have really, really damaging and long-term impacts. So things like talking about people in dehumanizing language, institutionalizing policies that treat people as less than human, those things can really create attitudes that then persist for a long time.

Just even looking back on American history, how could we not think that an institution that basically treated humans as less than human for 250 years, how could we think that that would not have a lasting effect two generations down the road? It's almost crazy to think the opposite, that it wouldn't have an effect.

So I think the caution for democratic theory or democratic governance is how to avoid that moving forward. How can we avoid the missteps that we made historically? You see some of the missteps happening right now with things like forced separation of families and this racialized rhetoric and dehumanizing rhetoric and this is a dangerous path. Obviously, it's different from the institution of slavery, but it's uncomfortably close and sometimes –

CHRIS HAYES: Yeah, the evil you do, the evil you do and the institutions you build and the ideology and language you construct to justify the evil you do will persist long after the institutions themselves are gone hundreds of years.

MAYA SEN: Yeah, exactly.

CHRIS HAYES: That's a really fucking terrifying thing to consider.

MAYA SEN: You see children at some of these rallies, and it's actually similar to what you saw around the turn of the century with racialized violence. And you see them parroting the words of their parents in ways that you know they don't really understand what they're saying, but they're soaking in these lessons. And these are lessons that they're going to carry forward with them for...

CHRIS HAYES: They're being passed down.

MAYA SEN: Yeah. We can build very, very accurate predictive models about people's vote choice at this point.

CHRIS HAYES: Yeah, it's crazy.

MAYA SEN: And the political parties know this, right? So it's not about changing people's minds anymore. It's about voter turnout. That, in itself, is sort of...

CHRIS HAYES: That is in some ways, and in a weird way, it's like when you go back to the beginning of the country's politics, they knew that then, too, right? I mean, they didn't have the models, but they knew who was in what camp, and the institutions and the politics got built around that.

MAYA SEN: The other thing that I'm seeing in the news right now that's really predicted by our book is this Georgia voter turnout stuff, actually speaking of voter turnout. When race and partisanship are so closely aligned, owing in part to the forces that we talk about in the book, it makes sense that voter suppression efforts would turn racial very quickly.

CHRIS HAYES: Yes, and it cultivates precisely this sort of institutional legacy, ideological legacy. So when you have Stacy Abrams in Georgia – black woman running against a white Republican – and I imagine that we could take the map of those Georgia county results and graph them onto the high-slave counties, low-slave counties and get some interesting matches.

MAYA SEN: Almost certainly, probably.

CHRIS HAYES: The book's called “Deep Roots, How Slavery Still Shapes Southern Politics.” It's by Matthew Blackwell and Maya Sen, who are here with me, and their third author, Avidit Acharya, who is at Stanford, who is not here in the studio. The book is really, really excellent. It'll blow your mind. It blew mine. Thanks a lot, guys.

MAYA SEN: Thanks for having us.

MATT BLACKWELL: Thank you.

CHRIS HAYES: So once again, I want to thank Maya Sen and Matthew Blackwell for that amazing conversation. The book, which you can get and I really recommend reading, it's really well done. It's called “Deep Roots, How Slavery Still Shapes Southern Politics.”

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