Political polarization has been increasing globally over the past few decades and is the focus of many recent academic studies. Given the pressing problems tied to political polarization, many scholars have attempted to identify the origins of our political divides. However, important questions remain about whether polarization is driven by politicians’ shaping the agenda for their electoral benefit or if elected officials are becoming more polarized as they follow public attitudes in hopes of being re-elected.

In The Roots of Polarization: From Racial Realignment to the Culture Wars, Neil O’Brian wades into this timely and important debate using a wealth of historical and contemporary data sources. O’Brian argues that polarization is not a top-down process led by political elites. Instead, political parties made key decisions around civil rights in the 1960s, which gave them less space to take opposing positions on a host of non-racial topics down the road. Specifically, Democrats’ decision to take liberal positions on racial issues made it so that they could only take left-leaning positions on a host of other topics to build a competitive electoral coalition. Once Democrats became tied to racial progressives with their support for the 1964 Civil Rights Act and the 1965 Voting Rights Act, Republicans were left with few options but to take a conservative position on racial issues during this period. In doing so, they too became largely constrained in the positions they could take in the future on other non-racial issues. Past decisions limited the electoral constituencies that each party could stitch together, thereby fueling polarized politics.

This process is carefully outlined and empirically assessed in the first two substantive chapters of the book. In these chapters, O’Brian convincingly shows that before the Civil Rights Movement, party identification was a weak predictor of numerous social attitudes. For example, in the 1970s, Democratic identifiers in public opinion surveys held the most conservative views on abortion, and liberals like Ted Kennedy were torn on which positions they should take on this defining issue.

American politics, however, was fundamentally realigned as a result of landmark racial legislation of the 1960s, which led voters to sort themselves around what are now quintessential liberal or conservative issues. O’Brian in Chapter 3 uses historical polling data from numerous sources including Gallup, The American National Election Study, The Harris Poll, and the General Social Survey to show that even when people did not know where parties stood on any particular area, a voter’s views on racial equality could predict what they thought about a significant number of social issues. For example, O’Brian’s analysis shows that racial attitudes are correlated with a host of other attitudes from pollution to the legalization of marijuana to strengthening the social safety net. When a person is liberal on racial topics, they are also more likely to take liberal stances on gun control, abortion, and even immigration. The same is true in reverse.

When parties became associated with either liberal or conservative positions on race, then, Stout shows that they were predestined to draw from a specific base of voters. These voters limited the positions that politicians could take on a host of issues. This led to more consistency in position-taking among politicians, fewer cross-pressured voters, and ultimately greater political polarization.

One of the strengths of Roots of Polarization is O’Brian’s ability to anticipate critiques and to consider alternative explanations. One question I had early in the book was why race and racial attitudes were so central to the origins of polarization in America? Could the abortion debates around Roe v Wade or the fights around healthcare in the 1990s have produced similar results? In Chapter 4, O’Brian explores this question through an examination of cross-pressured voters who hold both racially liberal positions and conservative positions on other issues (or vice versa). Through an analysis of panel data, O’Brian finds that people update their ideological positions to become consistent with their stances on racial topics. While he provides empirical support for this claim in Chapter 4, the book does a wonderful job throughout in explaining the unique significance of race in American politics and why it was and is such a potent organizing topic.

Once views on racial issues pushed the American people to organize themselves around various positions, O’Brian thoroughly demonstrates that it is voters who drive changes in position-taking amongst party leadership and not the other way around. In Chapter 6, O’Brian utilizes archival data from a variety of sources to counter the prevailing idea that politicians and interest groups shaped government attitudes on abortion. Instead, this analysis shows that the parties identified the voters most supportive of their position on this issue and collaborated with these groups to mobilize them. In Chapter 7, O’Brian uses the case study of Republicans’ hopes for immigration reform and the push-back they received from voters to show the constraints that politicians face when trying to move voters with opposing viewpoints to their position.

The Roots of Polarization is a well-written book that engages with many key debates in American politics. Its most obvious contribution is to answer the question of why we are polarized. By speaking to the structural antecedents that formed each party’s political base, O’Brian demonstrates that polarization is not just the result of politicians’ or the media’s decisions to divide the public at a given moment. Instead, it is something that is baked into the U.S. political system and requires a much more complex set of solutions than simply supporting moderate politicians and advocating for more resources for unbiased media.

O’Brian’s findings may also speak to a slate of recent studies, which demonstrate that racial resentment often spills over to shape political attitudes about non-racial issues like healthcare, gun control, and support for the January 6th rioters. Given that people have and continue to divide first on their positions towards race, it is not surprising that many of these studies find a link between racial resentment and topics that are not explicitly racial. This shows the enduring impact of racial attitudes on a wide array of political issues, and it takes seriously the idea that attitudes about racial issues are a central driver of polarization rather than merely a consequence.

While The Roots of Polarization will have a broad impact, my hope is that future research can pick up where it leaves off to explore a few unanswered questions. For example, I would be curious whether there are circumstances in which politicians and elites are able to direct voters rather than the other way around. O’Brian convincingly demonstrates that the parties’ stances on race significantly influenced the positions they could reasonably adopt on pre-existing and well-known issues like climate change and abortion. However, are there uncrystallized issues like COVID-19 where politicians can play a larger role in polarizing the public and shaping their views?

The Roots of Polarization urges us to consider how decisions made generations ago continue to shape modern American politics. The book’s unique racial realignment and party sorting hypothesis—along with its ability to blend historical and contemporary data seamlessly—make it a must read for anyone who is interested in fully understanding the current state of U.S. political affairs.