This article argues that a common pattern and set of dynamics characterizes severe political and societal polarization in different contexts around the world, with pernicious consequences for democracy. Moving beyond the conventional conceptualization of polarization as ideological distance between political parties and candidates, we offer a conceptualization of polarization highlighting its inherently relational nature and its instrumental political use. Polarization is a process whereby the normal multiplicity of differences in a society increasingly align along a single dimension and people increasingly perceive and describe politics and society in terms of “Us” versus “Them.” The politics and discourse of opposition and the social–psychological intergroup conflict dynamics produced by this alignment are a main source of the risks polarization generates for democracy, although we recognize that it can also produce opportunities for democracy. We argue that contemporary examples of polarization follow a frequent pattern whereby polarization is activated when major groups in society mobilize politically to achieve fundamental changes in structures, institutions, and power relations. Hence, newly constructed cleavages are appearing that underlie polarization and are not easily measured with the conventional Left–Right ideological scale. We identify three possible negative outcomes for democracy—“gridlock and careening,” “democratic erosion or collapse under new elites and dominant groups,” and “democratic erosion or collapse with old elites and dominant groups,” and one possible positive outcome—“reformed democracy.” Drawing on literature in psychology and political science, the article posits a set of causal mechanisms linking polarization to harm to democracy and illustrates the common patterns and pernicious consequences for democracy in four country cases: varying warning signs of democratic erosion in Hungary and the United States, and growing authoritarianism in Turkey and Venezuela.

Growing racial, ideological, and cultural polarization within the American electorate contributed to the shocking victory of Donald Trump in the 2016 presidential election. Using data from American National Election Studies surveys, we show that Trump’s unusually explicit appeals to racial and ethnic resentment attracted strong support from white working-class voters while repelling many college-educated whites along with the overwhelming majority of nonwhite voters. However, Trump’s campaign exploited divisions that have been growing within the electorate for decades because of demographic and cultural changes in American society. The 2016 presidential campaign also reinforced another longstanding trend in American electoral politics: the rise of negative partisanship, that is voting based on hostility toward the opposing party and its leaders. We conclude with a discussion of the consequences of deepening partisan and affective polarization for American democracy and the perceptions by both experts and the public of an erosion in its quality.

This article compares the dynamics of polarization in the eleven case studies analyzed in this special issue to draw conclusions about antecedents of severe political and societal polarization, the characteristics and mechanisms of such polarization, and consequences of severe polarization for democracy. We find that the emergence of pernicious polarization (when a society is split into mutually distrustful “Us vs. Them” camps) is not attributable to any specific underlying social or political cleavage nor any particular institutional make-up. Instead, pernicious polarization arises when political entrepreneurs pursue their political objectives by using polarizing strategies, such as mobilizing voters with divisive, demonizing discourse and exploiting existing grievances, and opposing political elites then reciprocate with similarly polarizing tactics or fail to develop effective nonpolarizing responses. We explain how the political construction of polarization around “formative rifts” (social or political rifts that arise during the fundamental formation/reformation of a nation-state), the relative capacity of opposing political blocs to mobilize voters versus relying on mechanisms such as courts or the military to constrain the executive, and the strategic and ideological aims of the polarizing actors contribute to the emergence of its pernicious form. We analyze the consequences for democracy and conclude with reflections on how to combat pernicious polarization.

With recent political developments sparking sharp divisions within democracies, an understanding of the dynamics of polarization is ever more necessary. Yet we still lack the tools necessary for its comparative study at the mass level. Finding that conventional measures of polarization as ideological distance between parties or among voters do not fully capture political polarization, we develop a new index of mass partisan polarization based on support and rejection of political parties by the public. We argue that measuring polarization over political parties allows us to capture divisions over a broader range of identities or issues which parties can represent or take positions on. Using Comparative Study of Electoral Systems data, our empirical validity tests support this argument. It is our hope that this index may facilitate the further comparative study of mass political polarization on a global scale.

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