One of the most moronic members of Congress was in the news recently when she proposed a “national divorce”. Red and blue states would go their separate ways. She’d have us remain one country, but the national government would have much less authority than it does now.

American politics being what it is these days, many of us, probably most of us, have thought it would be a good idea if those other states — the crazy ones — went off and formed their own damn country. Unfortunately, this would be a very difficult thing to do.

Back in 1861, the country was geographically divided between the North and South. The South  had slavery, its “peculiar institution”, and the North didn’t. But the division wasn’t that clearcut. There were five “border states” (Missouri, Kentucky, West Virginia, Maryland and Delaware, moving from west to east) that permitted slavery but didn’t secede from the Union. They’re the light blue ones below (the gray areas were relatively unsettled “territories” that hadn’t yet become states).

President Lincoln’s Emancipation Proclamation was only intended to end slavery in the eleven states that had seceded. It wasn’t until the 13th Amendment to the Constitution was ratified in 1865 that slavery was abolished everywhere. But geography made it relatively easy for the southern states to try to leave.

Dividing America by red and blue states is more complicated today. This map shows the results of the 2020 presidential election. The blue states voted for the Democratic winner; the red ones for the Republican loser. The red states are connected; the blue ones aren’t. And look at Georgia all by itself. (That’s where the Republican moron who proposes a national divorce was voted into Congress. Based on this election, she’d want to relocate.)

This way of portraying an election makes sense in terms of our obsolete Electoral College, since it requires each state to hold its own separate presidential election. In almost every state, a candidate gets all of that states “electoral votes” if they beat their opponent by one vote in that state’s election.

But a state-level map hides something important about American politics. After the 2004 election, the editors of a Seattle alternative paper called “The Stranger” wrote about our Urban Archipelago:

Look at our famously blue West Coast. But for the cities—Seattle, Portland, San Francisco, Los Angeles, and San Diego—the West Coast would be a deep, dark red. The same is true for other nominally blue states. Illinois is almost entirely red—Chicago turns the state blue. Michigan is almost entirely red—Detroit, Lansing, Kalamazoo turn it blue. And on and on. What tips these states into the blue column? Their urban areas do, their big, populous counties….

Liberals, progressives, and Democrats do not live in a country that stretches from the Atlantic to the Pacific, from Canada to Mexico. We live on a chain of islands. We are citizens of the Urban Archipelago, the United Cities of America. We live on islands of sanity, liberalism, and compassion—New York City, Chicago, Philadelphia, Seattle, St. Louis, Minneapolis, San Francisco, and on and on.

And we live on islands in red states too—a fact obscured by that state-by-state map. Denver and Boulder are our islands in Colorado; Austin is our island in Texas; Las Vegas is our island in Nevada; Miami and Fort Lauderdale are our islands in Florida. Citizens of the Urban Archipelago reject heartland “values” like xenophobia, sexism, racism, and homophobia, as well as the more intolerant strains of Christianity that have taken root in this country….

For Democrats, it’s the cities, stupid—not the rural areas, not the prickly, hateful “heartland,” but the sane, sensible cities—including the cities trapped in the heartland.

This map shows the 2020 election by county instead of state. The blue dots are the Urban Archipelago, the United Cities of America. (The map also shows how Biden managed to win by 7.5 million votes, unlike state-level maps that ignore how many people are in those states.)

Of course, not everybody in Los Angeles County or Miami-Dade voted for Democrats. But on top of all its other problems, a “national divorce” by state would strand millions of Democratic city dwellers in red Republican states free to become even more reactionary and dangerous to live in.

Even though un-uniting the United States is unlikely, thinking about the possibility helps us understand our country’s political geography. According to a 2019 paper by Will Wilkinson of the Niskanen Center, it’s all about cities and population density. The title of the paper is “The Density Divide: Urbanization, Polarization and the Populist Backlash”. Here’s his summary of his findings:

We’ve failed to fully grasp that urbanization is a relentless, glacial social force that transforms entire societies and, in the process, generates cultural and political polarization by segregating populations along the lines of the traits that make individuals more or less responsive to the incentives that draw people to the city. I explore three such traits — ethnicity, ideology-correlated aspects of personality, and level of educational achievement — and their intricate web of relationships. The upshot is that, over the course of millions of moves over many decades, high density areas have become economically thriving, multicultural havens while whiter, lower density places are facing stagnation and decline as their populations have become increasingly uniform in terms of socially conservative personality, aversion to diversity, and lower levels of education. This self-segregation of the population, I argue, created the polarized economic and cultural conditions that led to populist backlash [note: and the election of You Know Who in 2016].

Because the story of urbanization just is the story of a strengthening relationship between density, human capital and economic productivity, it’s also the story of relative small town and rural decline. The same process that has filtered better-educated, more temperamentally liberal whites out of lower density places has left those places with less vibrant economies, but also with more place-bound, ethnocentric populations.

It’s no shock that leavers leave and stayers stay. What’s surprising is that, if you’re white…,  the personality traits that make you more or less inclined to leave or stay — that make you more or less magnetized to the rising attractive force of the city — also predict how socially conservative or liberal you’ll tend to be, and which political party you’ll tend to support.

So the pull of urbanization has segregated us geographically on those traits, and it has done it so thoroughly that Democratic vote share now rises, and Republican vote share drops, in a remarkably linear fashion as population density rises. The relationship between density and party affiliation is, with few exceptions, similar everywhere — in “red states” and “blue states,” in sprawling metro regions and bucolic small towns — and majorities tend to flip at the density typical of a big city’s outer suburbs. I call this partisan polarization on population density the “density divide.”

When populations segregate geographically on traits relevant to ideology and party affiliation, political polarization is sure to follow. The increasing concentration of the economy in big cities, which is both a cause and effect of urbanization, amplifies this polarization. Rising prosperity reliably produces a liberalizing, tolerant, positive-sum mood. Material insecurity, in contrast, tends to elicit a grim, zero-sum, us-or-them mindset. Because the sunshine of prosperity has become increasingly focused on urban populations, lower density white populations — which, thanks to the sorting logic of urbanization, are already more conservative and ethnocentric — have been left with objectively darkening prospects and a mounting sense of anxiety that is, at once, economic and ethno-cultural.

This combination of conditions created a political opportunity [a certain orange demagogue]  managed to exploit. Because urbanization is reshaping societies everywhere around the world, it has created similar conditions, and similarly illiberal strongman leaders, in other countries as well. If we’re going to be able to do anything about the acrimony of polarization and the peril of ethno-nationalist populism, we’re going to have to get the story straight. This cross-disciplinary account of the social and psychological forces behind the density divide is my preliminary attempt to put us, finally, on the right track.