American political observers express increasing concern about affective polarization, i.e., partisans' resentment toward political opponents. We advance debates about America's partisan divisions by comparing affective polarization in the US over the past 25 years with affective polarization in 19 other western publics. We conclude that American affective polarization is not extreme in comparative perspective, although Americans' dislike of partisan opponents has increased more rapidly since the mid-1990s than in most other Western publics. We then show that affective polarization is more intense when unemployment and inequality are high; when political elites clash over cultural issues such as immigration and national identity; and in countries with majoritarian electoral institutions. Our findings situate American partisan resentment and hostility in comparative perspective, and illuminate correlates of affective polarization that are difficult to detect when examining the American case in isolation.

While dislike of opposing parties, that is, affective polarization, is a defining feature of contemporary politics, research on this topic largely centers on the United States. We introduce an approach that analyzes affective polarization between pairs of parties, bridging the US two-party system and multiparty systems in other democracies. Analyzing survey data from twenty Western democracies since the mid-1990s, first, we show that partisans' dislike of out-parties is linked to elite policy disagreements on economic issues and, increasingly over time, also to cultural issues. Secondly, we argue and empirically demonstrate that governing coalition partners in parliamentary democracies display much warmer feelings toward each other than we would expect based on elite policy (dis)agreements. Third, we show that radical right parties are disliked much more intensely than we would expect based on policy disputes and coalition arrangements. These findings highlight the policy-based and institutional underpinnings of affective polarization.

Comparative politics scholars argue that consensual democratic institutions encourage power-sharing that promotes “kinder, gentler” politics. We uncover one reason why this is the case: elite inter-party cooperation in consensual systems is associated with reduced inter-party hostility in the mass public. This is because governing parties’ supporters feel much more warmly toward their coalition partner(s) than we can explain based on policy agreement alone. Moreover, these warm affective evaluations linger long after the coalition itself has dissolved. We substantiate our arguments via analyses of CSES survey data from 19 Western democracies between 1996 and 2017, showing that current and past co-governance is associated with substantially warmer inter-party affective evaluations. This implies that electoral systems which encourage coalition governance may defuse partisan hostility.

Concern over partisan resentment and hostility has increased across Western democracies. Despite growing attention to affective polarization, existing research fails to ask whether who serves in office affects mass-level interparty hostility. Drawing on scholarship on women’s behavior as elected representatives and citizens’ beliefs about women politicians, we posit the women MPs affective bonus hypothesis: all else being equal, partisans display warmer affect toward out-parties with higher proportions of women MPs. We evaluate this claim with an original dataset on women’s presence in 125 political parties in 20 Western democracies from 1996 to 2017 combined with survey data on partisans’ affective ratings of political opponents. We show that women’s representation is associated with lower levels of partisan hostility and that both men and women partisans react positively to out-party women MPs. Increasing women’s parliamentary presence could thus mitigate cross-party hostility.

Affective polarization measures account for partisans’ feelings towards their own party versus its opponent(s), irrespective of how frequently partisans encounter co-partisans versus out-partisans in everyday interactions and public discourse. However, the social impact of cross-party hostility depends on both the intensity of dislike and the frequency with which this comes into play. We develop an affective fractionalization measure that accounts for both factors and apply it to longitudinal survey data from 20 Western publics. This fractionalization perspective implies that the partisans in countries with fewer dominant parties – notably the United States – may interact less frequently with out-partisans, which might cushion the negative social impact of inter-party animosity. At the party level, partisans of smaller and more radical parties are particularly isolated because they strongly dislike out-partisans but are highly likely to interact with them. Over time, affective fractionalization has increased in most countries, partly due to rising cross-party hostility but primarily because most Western party systems have become increasingly fragmented.