This past weekend I participated in a fascinating conference entitled A Republic, if We Can Keep It, sponsored by Cornell’s Center for the Study of Inequality and New America. Participants included academics, journalists, analysts, and others, all brought together to debate the state of American democracy—with particular emphasis on understanding American democracy in comparative perspective.

One issue that frequently comes up in such discussions is American exceptionalism. For the purposes of that particular discussion on the state of American democracy, the relevant question is, does the United States have some sort of exceptional quality that explains the durability of its democratic institutions over more than two centuries? The link earlier in this paragraph gives plenty of examples of what that exceptional quality might be: its religious history, its English cultural roots, the specific nature of the founding, the tradition of republicanism, and so forth.

As someone whose research focuses on comparative politics (i.e., the rest of the world), I am duty-bound—professionally-speaking—to be skeptical of any claim of American exceptionalism. But there is one way in which I think that the United States really is exceptional, and it does matter for understanding American democracy, past and present. Specifically, the United States is the world’s only settler colony endowed with an enduring legacy of plantation slavery.

It is possible to speak, in general terms, about two types of colonies. Settler colonies such as Canada, Australia, and Uruguay featured large-scale migration of Europeans, coupled with the near complete annihilation of their indigenous population. These are colonies in which European settlers were able to recreate European social and political institutions. Another type of colonial economy relied on large-scale plantation labor or commodity extraction, almost always supported by slavery (as in the Caribbean and Peru), significant forms of labor repression (as in Indonesia and Angola), or general neglect (as in Malaysia). These are colonies in which indigenous or African slave populations outnumbered the European population.

The idea that there were difference in colonies based on whether or not Europeans settled en masse there is certainly not new. Acemoglu, Johnson, and Robinson’s landmark work on “The Colonial Origins of Comparative Development” relied on a simple distinction between those colonies where Europeans could settle (and hence built European institutions) and where they could not due to disease (and hence built extractive institutions).

My point, however, is not about the origins of development or the mortality of settlers. It is about the legacies of such social structures after independence. The United States is unique—it is exceptional—in the specific sense that it combines both the institutions of settler colonialism and the legacy of large-scale plantation slavery. The closest analogues for the United States would be Brazil and (to a lesser extent) South Africa, and Anthony Marx’s Making Race and Nation takes up this comparative project explicitly. Other settler colonies, like Argentina, have slave histories but relatively few descendants of African slaves as a proportion of their total population today.

Understanding American exceptionalism this way matters for understanding American democracy today because it reminds us that democratic institutions can coexist with racially exclusive policies and institutions, and that American democracy has always had to deal with this legacy. No other settler colony must confront a legacy of slavery in this way. Scholars of American politics from Hochschild, Weaver, and Burch to King and Smith have used the term “racial order” to describe “the beliefs, institutions, and practices” that define race and politics in the United States. In principle, every country has its own racial order; America is exceptional in how its racial orders must confront both European political institutions and the legacies of plantation slavery at scale.

That confrontation between European institutions and plantation slave legacies has generally not favored the latter, and understanding why allows us to characterize just what it is that American democracy represents. Prior to the abolition of slavery, and then again under Jim Crow, and in various ways until today, American democracy has operated by restricting the very citizenship of black Americans. Dankwart Rustow’s argument that democracy requires mass agreement on who the members of a political community are has the uncomfortable implication that it might be that mass agreement about the non-membership or non-citizenship of certain groups provides the foundation for durable democratic institutions. But these democratic institutions do not represent all denizens of a given territory.