How does the scale of a polity influence its politics? This is a question that has long fascinated those who have asked what type of polity is most suitable to being a republic. In my opinion, John Gerring and Wouter Veenendaal have written one of the most insightful contributions on this topic since Robert Dahl and Edward Tufte’s classic Size and Democracy, which was published almost 50 years ago (in 1973). Although there have been many excellent contributions on this topic, Gerring and Veenendaal provide us with a particularly systematic and comprehensive examination of the problem. Their basic approach is to use data on a range of political outcomes, both at the national and subnational level, and then see how these are correlated with the size of a country’s (log) population. The authors take pains to emphasize that scale is, of course, endogenous, and so what they provide us with is a set of broad cross-sectional relationships that can nonetheless be informative. Although these statistical estimates form the backbone of the study, Gerring and Veenendaal also provide the reader with a wealth of other types of evidence, including, among other things, the results of interviews with a large number of officials. In short, there is an immense amount of insightful material in this book.

The authors begin their study by outlining what they see as the traditional approach, dating back to Plato and extending to Dahl and Tufte, which sees large scale as detrimental to a republic. In the words of the authors, in this tradition, “City-states are beloved while empires are loathed” (p. xix). They then contrast this traditional approach—one they see as still dominant—with the Madisonian approach from Federalist 10, which extols the virtues of scale because it is said that that scale, among other things, helps weigh against the emergence of a tyranny of the majority because larger polities have more distinct parties and interests.

The empirical conclusions the authors reach are nuanced, and for this reason, neither those who are fervent adherents of Federalist 10 nor those who adhere to the traditional view will feel entirely satisfied. But they should be. It turns out that the world is a bit more complicated than either of the two existing views make it out to be. Larger-scale societies tend to be less cohesive, to have less trust in government, and to have lower levels of political participation—all of which would have a familiar ring to the traditionalists. At the same time, small scale can also be associated with phenomena we think of as being undesirable, such as increased particularism and less contestation of power. These outcomes fit better with the Madisonian view. The authors show this using ordinary least squares regressions that pool alternatively a large number of countries or a large number of subnational units. This is done in a way that is particularly comprehensive and clearly laid out. The authors do offer instrumental variables estimates where land area and agricultural suitability are used as instruments for population size, but they shy away from emphasizing these given the strong assumptions necessary to satisfy the exclusion restriction. The authors do not claim to offer a natural experiment.

After reaching the above conclusions, as well as many others that I do not have the space to do justice to here, the authors provide us with a final chapter that takes stock and looks forward. Here, they take pains to emphasize that if we want to understand the consequences of scale, then we need to recognize that it is a distal cause. For any one of their results, there may be multiple mechanisms operating simultaneously. They then take steps toward a more general theoretical framework by suggesting how increased scale at any level is likely to increase the coordination problems that citizens face.

This book is thought provoking not only for the conclusions the authors reach but also for what their findings suggest about a future program for research in this area. First, drawing on the conclusions from Gerring and Veenendaal, we should be asking how and when a large society, such as the United States, might be able to overcome the costs of scale while still enjoying the benefits. Second, given the evidence presented here that scale may matter in very important ways, after reading this book, it is ever more important to ask what determines scale in the first place.

The conclusions that Gerring and Veenendaal reach prompt us to first ask what can be done to mitigate the negative effects of scale. Let us take the conclusions of the authors that increased scale is associated with less trust in government, a phenomenon that is seen both for the size of countries as well as for the size of cities. This represents an average effect, but there is clearly much variation that remains unexplained purely by population size. As an example, based on Eurobarometer evidence, Germany, with a population of 83 million, has much higher trust in government than does Greece, with a population of only 11 million. If scale is not fate, then it opens up the possibility that societies might actually be able to do something to counteract its negative effects—for example, by investing in policies and institutions that might promote cohesion. In sum, we need to know what different polities have done over time to cope with the challenge of scale.

The second question for the future is how scale is determined in the first place. If we follow the authors, as we should do, in accepting that there is no convenient instrumental variable that explains where scale comes from, we should still be deeply interested in this question. One of the most intriguing findings presented by Gerring and Veenendaal is that the variance of polity size is much greater than is the range of size for other types of human organization—be they universities, firms, interest groups, or even political science departments. If in other domains there seem to be forces that produce less dispersion in organizational size, these same forces seem to operate to a much lesser degree in politics. The authors conjecture that this may be because political entities are subject to weaker efficiency constraints. I would suggest that one could also use the core argument made by the authors—that there are tradeoffs when it comes to scale—to explain why, in the contemporary world, countries of vastly different sizes all seem to survive, or at least have survived so far. Even so, although this might help to explain the stability of the system, we are still lacking an explanation of the historical process that led to the emergence of these polities of vastly different sizes in the first place.

There is so much to recommend in this book. It will be of interest to a broad range of political scientists in all four of the traditional subfields of our discipline. Gerring and Veenendaal have provided us with the most comprehensive analysis to date of the politics of scale. Their findings are enlightening, and they point to important avenues for future research.