In The Great Experiment: Why Diverse Democracies Fall Apart and How They Can Endure, political scientist Yascha Mounk asks the most far-reaching political question of our age: can democracies that are ethnically diverse survive? Mounk calls it “the great experiment” because, although democracies throughout the world are becoming more ethnically diverse, the only example of such a democracy that has sustained itself for a significant period of time is the United States—and American democracy itself is in trouble. Potential solutions to this problem are limited, for reasons which Mounk baldly and correctly states: Turning back the clock is not an option, because “effective ways to halt the great experiment are virtually certain to be morally intolerable.” Deporting hundreds of thousands, let alone millions of citizens is a non-starter. Countries must work with the diversity they already have.

There is much to admire about The Great Experiment, starting with the book’s readability. Mounk writes beautifully. A German-born American citizen who teaches international affairs at the Johns Hopkins’s School of Advanced International Studies in Washington, D.C., he has wide-ranging knowledge about the experiences of diverse nations throughout history and across the globe. He uses many narrative illustrations drawn from history and personal experiences. (Whether The Great Experiment takes discursiveness too far is a matter of taste—I enjoyed the stories while often wishing Mounk would get on with it.) I also admire Mounk’s wisdom about the alternative futures we might seek. He is a self-described man of the center-Left who, like Christopher Lasch and George Packer, writes perceptively about the lives of people outside the cognitive elite. He eloquently discusses the roles of patriotism and religion in sustaining democracies, and he chides the Left for disdaining those cultural bulwarks. Mounk’s critique of the two leading metaphors for dealing with diversity—the melting pot and the salad bowl—made me rethink my own position. His alternative metaphor—the public park, in which different groups amicably pursue their various activities—provides a versatile framework for thinking about how diversity might be handled. These are only a few of the many virtues of The Great Experiment.

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For this reader, however, The Great Experiment felt irrelevant to the situation facing the United States. America’s diversity problems are incomparable to those facing west European countries.

The first disparity between America and western Europe is that whites continue to be an overwhelming majority of the population everywhere in western Europe. Ten west European countries have populations that are over 90% white. The most diverse country in west Europe by this measure is the Netherlands, with “only” 84% whites. Compare that with the United States, where whites amount to only 60% of the population and are on their way to becoming a minority. The reason this is important has nothing to do with whiteness or European culture. Rather, Europe’s white population matters because a large ethnic majority can unilaterally set the terms of assimilation by minorities. This is as true of the Chinese majority in Singapore as of the white majority in Norway. The countries of western Europe still have the option to do what the United States did throughout its history until the 1960s: energetically socialize immigrants into the culture of their new country and require, as Theodore Roosevelt famously put it for the United States, that an immigrant’s naturalization be “predicated upon the person’s becoming in every facet an American, and nothing but an American.” Whether any west European nation will do this is an open question, but it is an option for them. It is no longer an option for the United States.

The second disparity is the size of the individual ethnic minorities. No one ethnic minority in any west European nation is large enough to be a political force on its own except France’s North African population (estimated at 10%). Everywhere else, the largest discrete ethnicity is a few percent of the population. A few percent of the population cannot become a political force on its own, and different immigrant ethnicities seldom form alliances. In contrast, the United States has two large and politically powerful minorities: Latinos (19% of the population) and blacks (12%). Asians (6%) are emerging as another.

The third disparity is religion. European whites in western Europe are now effectively secular. In the United States, religion is still a cultural and political source of division.

The fourth disparity is ideological. No west European country is engaged in an ideological struggle over the proper role of government—social democracy is the consensus political ideology. America has been fighting a political war about the proper role of government since the rise of Progressivism in the late 19th century.

A fifth disparity usually goes unmentioned, despite its considerable importance: geographic size. Even limited to the contiguous Lower 48, America covers 3,131,358 square miles. The largest nation in west Europe is France, less than 7% the size of the Lower 48. The average west European nation is less than 3% the size of the Lower 48. The vast geographic area of the United States facilitates forms of falling apart that are impossible in the countries of Western Europe.

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I hope that The Great Experiment attracts readers in western Europe, where many of Mounk’s insights about how to help diverse democracies survive can be applied. At the same time, however, I see little in the book that applies to America’s predicament.

My deeper problem with The Great Experiment is that it is ultimately unserious. Anyone who writes about the problems associated with ethnic diversity must plunge into topics that will arouse the fury of the progressive Left. There’s no choice. Too much of the relevant knowledge is intertwined with scholarly literatures that are on the progressive Left’s Index Librorum Prohibitorum. Three of those literatures, each of which amounts to a large body of rigorous work, are ignored in The Great Experiment: the role of evolved human nature, the relationship between social trust and ethnic diversity, and ethnic differences in social behavior.

Mounk’s first sin of omission is to disregard evolutionary psychology. He correctly acknowledges that humans are “groupish” (his word), and he probably knows more than he lets on. He uses the phrase “we are wired…” with regard to groupishness, tacitly acknowledging an evolutionary basis. But he doesn’t explain why humans are groupish or why he doesn’t propose solutions for groupishness.

If it were merely a matter of terminology, Mounk’s preference for using “groupish” wouldn’t be a problem. But one of the Left’s most crippling errors for a century now has been to discount the importance of innate and intractable human nature, insisting instead that human tendencies are malleable and that the behavior of large numbers of humans can be changed by design given the right social policies. This mindset persists despite Steven Pinker’s devastating critique of it in his bestselling The Blank Slate: The Modern Denial of Human Nature (2002), and despite 20 years’ worth of subsequent genetic findings that reinforce Pinker’s case. The Great Experiment needed a short section in which Mounk, who writes so persuasively, openly allied himself with Pinker. Mounk could have pointed out to his audience the many ways in which human nature, shaped by evolution, constrains the options for solutions to the problem of diverse democracy. But it probably wouldn’t have had much effect—apparently The Blank Slate didn’t—so I’ll call this omission a venial sin.

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The second sin of omission is closer to mortal: ignoring the empirical literature on ethnic diversity and social trust. “Social trust” refers to humans’ confidence in the good faith and good will of those around them. This is the kind of confidence that allows neighbors to leave the front door unlocked when leaving home for the afternoon, encourages people to do good deeds in the expectation that eventually they will be directly or indirectly reciprocated, and enables sellers to extend credit to buyers. Writ large, social trust is indispensable to an environment in which communities, capitalist economies, and democracy itself can flourish—a theme that has been developed by such eminent scholars as Edward Banfield in The Moral Basis of a Backward Society (1958), Francis Fukuyama in Trust (1995), and Robert Putnam in Bowling Alone (2000).

The problem is that ethnic diversity in a community significantly erodes social trust, not only between different ethnic groups but also among people within the same ethnic group. This ominous relationship was first documented in 2007 by Robert Putnam in “E Pluribus Unum” (Scandinavian Political Studies). By 2020, a meta-analysis of the relationship (“Ethnic Diversity and Social Trust,” Annual Review of Political Science) could call upon 87 separate studies. All 87 found a statistically significant negative correlation between ethnic diversity and social trust—an astonishing statistic for sociology or psychology, notorious for published findings that don’t replicate even once. The magnitude of the relationship differed across studies and is variously exaggerated or minimized by ideologically motivated commentators, but a serious discussion of why diverse democracies fall apart requires that the findings of the literature be incorporated. The Great Experiment doesn’t even mention that the relationship exists.

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the third sin of omission, ignoring the literature on ethnic differences in social behavior, is definitely mortal. Social behavior refers to the constellation of ways in which people act with respect to social institutions (marriage, civic activities, religious activities) and places (workplaces, schools, sidewalks, public parks, or others’ homes). The question regarding Mounk’s topic is whether social behavior varies by ethnicity, and the answer is yes on a host of behaviors. If the differences were small, the implications for sustaining a diverse democracy would also be small. For America’s East Asians and South Asians, the differences with whites are, in fact, small. For Latinos, they usually vary from small to moderate. For blacks, they usually vary from moderate to large.

To illustrate, I use one of the most important social behaviors: marriage. The following numbers refer to the percentage of adults aged 20 and over who are in heterosexual marriages with the spouse present, using data from the Census Bureau’s American Community Surveys for 2013–2020. Asians had the highest marriage rate (61%), followed by whites (54%), Latinos (44%), and blacks (28%)—a huge difference from top to bottom. Since marriage rates are known to increase along with education, it may be asked if the ethnic differences persist for people with high school diplomas, associate’s degrees, bachelor’s degrees, master’s degrees, and professional degrees. In the case of whites and Asians, the differences ranged from zero to five percentage points across those educational levels—small. In the case of Latinos and whites, the differences ranged from nine to 13 percentage points—moderate. In the case of blacks and whites, the differences ranged from 18 to 24 percentage points—large.

This is not the place to analyze how differences of these magnitudes affect the prospects for a successful diverse democracy. Rather, Mounk’s book was an appropriate place to analyze them—or at least mention them. The same may be said of ethnic differences in seeking jobs, student behavior in the classroom, participation in the political process, or volunteering for local charities. In combination, they must figure into any assessment of the prospects for America’s diverse democracy. But even in combination, the indicators I mentioned pale in significance when compared with ethnic differences in the social behavior that has the most dramatic effects on the formation and functioning of communities: crime, and especially violent crime.

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It has been known for decades that ethnic differences in crime rates exist, but the size of the differences for the nation as a whole are much smaller than the differences within cities—numbers that the FBI has chosen not to publish. The “open data” movement in the early 2010s led many cities to publish complete databases of all arrests, available for download by anyone with a computer and internet access. For 13 of these cities, the arrest databases included the race of the arrestee. I reported the results in my book Facing Reality: Two Truths About Race in America (2021). The black-to-white ratio for violent crime arrests across all 13 cities averaged 10:1. In New York, Los Angeles, Chicago, and Washington, the ratios were 12:1, 9:1, 14:1, and 20:1 respectively. The Latino-to-white ratios were smaller, but usually big enough to be significant, with a mean of 3:1 across all 13 cities. The Asian arrest rate was about the same as the white rate in New York City and much lower in the other 12 cities. I should add that extensive scholarship establishes that racial differences in arrests correspond to differences in actual criminal activity, not police bias.

Mounk’s discussion of crime consists mainly of documenting that crime among immigrants is often exaggerated, which is true. But when it comes to ethnicity, he limits himself to lamenting that blacks are incarcerated and killed by police at higher rates than their proportion of the population, without mentioning ethnic differences in crime rates. All by itself, Mounk’s failure to confront ethnic differences in crime would lead me to conclude that The Great Experiment is unserious.

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I am guilty of that most aggravating habit of reviewers, criticizing a book for not being the book the reviewer wanted to read. Was it indeed obligatory for Mounk to write about the three literatures he ignored? I can imagine a plausible scenario that says no.

Suppose that Mounk’s goal was to lead people on the Left to reconsider their prior assumptions about why anti-democratic political trends are spreading throughout the West. If he had discussed the constraints of human nature, the negative effect of ethnic diversity on social trust, and ethnic differences in social behavior, he would have lost the readers he sought to persuade. I empathize with what might have been Mounk’s rationale in leaving some things unsaid. I have been in similar situations and self-censored in similar ways.

Events since the summer of 2020 have led me to abandon that way of thinking. The United States is indeed in danger of falling apart. To the task of averting that catastrophe, Yascha Mounk has contributed the right metaphor—the public park—for a successful diverse democracy. His optimism that his vision can be realized has an important truth going for it: the great majority of Americans of all ethnicities are honest, well-meaning, hard-working people who would like to get along with everyone else. His evidence for progress that has been made on a few fronts is accurate.

And yet. The United States in 2022 is a deeply riven nation. What were once seen as political arguments are now seen by both Left and Right as a Manichean struggle between good and evil. Ethnic diversity feeds into that polarization in complicated ways. The present crisis of American democracy—I think “crisis” is warranted—demands a clear-eyed understanding of the ways in which some differences in ethnic groups and some sources of political polarization are never going to be resolved because they are grounded in realities that governments cannot change. Incorporating those realities into policy reforms could give us a realistic chance of creating Mounk’s public park. Ignoring them guarantees failure.