In her book, Karen Long Jusko develops a novel theory of party entry and applies it to explain when and where political parties that represent the poor emerge. Who Speaks for the Poor? claims that these parties enter politics only if poor voters become newly pivotal in a sufficient number of districts. The geographical distribution of poor voters at critical times in history leads to the emergence of different party systems, with downstream consequences for social policy. This work is outstanding in its ambition, creativity, and rigor. It addresses several of the classical debates in comparative politics, spells out the theoretical argument with care, and condenses years of empirical work that carefully tests the key predictions of the theory using rich historical data. With the publication of the book, Jusko establishes herself as one of the world’s most authoritative experts in the origins of party systems and the political representation of the poor.

The key decision makers in this account are political entrepreneurs, who may be policy demanders or office seekers, and who are intensely sensitive to the incentives provided by the contexts in which they operate. When party entry is difficult because most of the electorate is attached to established parties, it is unlikely that entrepreneurs bear the costs of organization and mobilization. Conversely, they are more likely to invest in running for office in districts that have experienced large changes in the electorate, where voters who are unattached to existing party networks abound. Voters, in strong contrast to strategic entrepreneurs, decide which party they support based on their attachment to existing partisan networks or, if they are not attached, on their membership in social groups. Once they are embedded in partisan networks, they change alliances only under exceptional circumstances.

Although the theory is general, the author applies it to explain the emergence of poor people’s parties. Societies have three key income groups: the poor, the middle-income people, and the rich. The poor are pivotal or decisive in districts where their number is sufficiently large to win elections. Weaving the different arguments together, Jusko’s first central claim is that new parties that represent the poor only enter politics when a sufficient number of districts simultaneously experience demographic change that makes the poor newly pivotal. This could occur because of different circumstances, such as migration, suffrage expansion, or sharp changes in local economic conditions that set voters free of their previous loyalties. The type of party that enters politics also depends on the characteristics of districts. Agrarian parties are formed if newly pivotal poor voters are located in rural areas, but if these poor voters are in urban areas, the new parties will be social democratic.

This new theory has several remarkable merits. It addresses the question of how structural forces, in this case demographic change, translate into political change by stressing the role of political entrepreneurs, described as bystanders shut out of party systems and waiting for opportunities to break in. Thus, it brings political agency to a structural account. It incorporates a specific feature of electoral geography, the spatial distribution of income groups, into a rigorous analysis of party entry. It makes precise predictions about the timing of party entry. And it attempts to provide a mechanism that explains the freezing of party systems long noted in the literature. The theory depicts party systems as being in equilibrium unless very specific and historically rare conditions are met.

A less satisfying aspect of Jusko’s argument is that the key independent variable, population change, is always the result of other processes of very diverse nature (migration, suffrage expansion, economic change). This theory about how exogenous shocks shake party systems out of equilibrium focuses on the intermediary mechanism without giving much attention to the nature of the shocks. It is also a one-dimensional theory of party competition that obviates how other cleavages undermine class voting (such as religion or alternative national identities), but at the same time does not explain what the content of political struggle is (if not the distribution of income between the rich and the poor nor alternative dimensions of conflict) in cases such as the United States that, according to this book, never saw the emergence of a large poor-people’s party.

Having said that, the main claims are backed with a masterful empirical analysis. Jusko first demonstrates that in 15 countries since the 1880s, more new parties entered politics in periods with large rates of local population change. One of the central contributions of the book is the mobilization of historical data to test the claims in four case studies: the Populist Party in the United States, the Cooperative Commonwealth Generation and the Social Credit in Canada, the Labour Party in the UK, and the Social Democratic Party in Sweden. The work invested in collecting statistics on income and population change at the subnational level is painstaking, and Jusko also backs up key assumptions of her model, in particular that elites make strategic calculations about party entry, through qualitative narratives. The thorough analyses of census data and other historical sources provide abundant evidence that parties that represent the poor were more likely to enter electoral competition in districts that experienced large increases in poor voters.

The second central claim of the book is that electoral geography has implications for redistribution and can help explain why some democracies offer less generous social policy than others. Here, the argument becomes less precise, and it is unclear if it is past or current electoral geography that matters, or both. As a key transmission mechanism, Jusko argues, historical electoral geography affects social policy through the legacies on party systems. Social policies are more generous if parties that represent the poor managed to enter politics in critical windows of opportunity that mostly occurred in the late nineteenth century. Because districts in the United States became very large and socially heterogeneous in the twentieth century, however, the conditions never arose again for a poor people’s party to enter politics after the failed attempt of the Populists.

There are several surprising features about these claims. The argument seems specifically tailored to explain American exceptionalism, or the absence of a poor people’s party in the United States, but it does not engage with alternative explanations of the low generosity of social policy, and notably with the history of race and the disenfranchisement of African Americans. The theory would seem to suggest that profound and geographically unequal shocks, such as the Great Depression and deindustrialization, should invite the entry of new parties, but the extent of changes in electoral geography in other critical historical periods is not addressed, leading to a big 100-year jump. The complete realignment that occurred in American politics, where most states that supported a party in 1896 went for the opposite party in 2000, is hard to reconcile with the strong emphasis on continuity, suggesting that parties are quite capable of changing the policy positions they offer even if their labels formally remain unchanged.

A much more convincing but distinct claim is that the contemporary geographic distribution of the poor is relevant because legislators have more incentives to be responsive to the poor if they are pivotal in a large number of districts. This point is brilliantly illustrated with the contrast between the United States and France, a system in which poor voters are more geographically concentrated and which has more generous social policies. The last chapter also demonstrates that social policy is more generous where the poor are distributed in space in ways that maximize their electoral power. The exact connection between the two parts of the book remains puzzling, though. Given that the mechanism for ascertaining why contemporary geography matters is straightforward (the incentives of legislators to defend the interests of their constituencies), it is unclear why the theory of party entry is necessary for understanding variation in social policy.

In spite of inevitable shortcomings, Who Speaks for the Poor? is relevant for a broad audience because it engages with several of the most crucial big questions in political science research: When and where do new parties enter politics? Why do political parties represent the interests of some social groups but not others? Why is the welfare state more generous in European countries than in the United States? In a time of ever-smaller research questions, this book is of a rare broad scope. For this, Jusko is to be commended.