The dynamics of political polarization

A number of trends in national and international politics greatly affect our capacity to achieve the cooperation that will be necessary to address the challenges facing society over the coming decades. These involve the interplay among partisanship and party loyalties within countries, populism, and polarization within and among nations. The trends are widespread and seem to be reshaping politics across the globe. They are inherently systems-level phenomena, involving interactions among multiple component parts and the emergence of broaderscale features; yet, they have been inadequately explored from that perspective. To make progress in understanding these issues, political-science research stands to benefit from insights from other disciplines, including evolutionary biology, systems science, and the disciplines concerned with the fair and efficient provision of public goods of all kinds, but especially those affecting the shared environment and public health. These other disciplines, in turn, stand to gain equally from the perspective developed in political science. In viewing political systems as complex adaptive systems, we can gain a new understanding of the forces that shape current trends, and how that knowledge might affect governance strategies going forward. Extreme polarization is a dangerous phenomenon that requires greater scientific attention to address effectively. This Special Feature of PNAS draws on this relatively new interdisciplinary field, featuring original joint research from collaborating political scientists and complex systems theorists. Each paper is a true partnership among the different disciplines and illustrates the benefits of closer ties between complex systems and social science. The papers explore the emergence of patterns and structures in societies and the linkages among individual behaviors and societal benefits across scales of space, time, and organizational complexity. The COVID-19 pandemic provides the most recent examples of how patterns of polarization in societies interact with our abilities to solve societal challenges. The main goal of the Special Feature is to deepen our understanding of the dynamics of political polarization and related trends, and especially the interplay among these processes at multiple scales, from the local to the international. The papers cover many different aspects of this issue and do so from different systems-level perspectives, providing a broad view of the problem. The papers explore the impact of information flow networks, the diverse nature of national governance systems, the role of the media, and the dynamics of party sorting. They pose a number of key questions. Do the dynamics of such systems follow a natural progression of polarization and collapse, similar to Schumpeter’s economic theories (1)? How do migration, globalization, and new technologies, such as the internet, affect the trends? Does an extension of Duverger’s Law (2) foreshadow a natural tendency toward polarization in nations with two-party systems, like that in the United States, undercutting Madison’s dream (3)? Duverger’s Law argues that a system like that of the United States, based on a plurality rule on a single ballot, will lead to a two-party system, while Madison hoped for a system that would “break and control the violence of faction” (3). The Special Feature arose from a series of workshops in which the issues were aired, collaborations were developed, and earlier versions of the papers received constructive feedback. It became clear from those discussions that even the definition of polarization has manifold aspects, that some degree of polarization is likely healthy in sharpening issue differences in any society, and that there have been historical fluctuations in polarization at all levels, within and among nations and peoples. What is clear, though, is that it is essential to understand the causes and consequences of polarization if we are to deal with regional, national, and global problems that we will face in the coming years. The Special Feature includes 11 individual articles, incorporating both novel research and Perspectives. In addition, Jenna Bednar (4) provides a Perspective embedding the contributions within the