Political polarisation has emerged as one of the most pressing challenges for advanced democracies in recent decades. Across the Atlantic, public life is increasingly dominated by partisan divides, growing social hostility, and widespread erosion of trust in institutions. These trends carry particularly significant consequences for the EU and its member states. Unlike the US, where polarisation is channeled into a two-party system, Europes context is shaped by multiparty competition that operates simultaneously at national, regional, and supranational levels. This makes polarisation more complex and multifaceted, as it not only influences electoral outcomes but also affects the stability of coalition governments, the cohesion of European integration, and the broader ability of democratic systems to provide inclusive and sustainable prosperity.
In recent years, the academic literature has expanded rapidly in an effort to understand these developments. Early studies largely focused on ideological extremity, describing polarisation as a widening gap between the left and the right. However, subsequent work has emphasized that polarisation goes far beyond ideology, extending into affective and identity-based dimensions (McCarty et al., 2006; Iyengar and Westwood, 2015; Funke et al., 2016). In increasingly polarised environments, politicians tend to adopt uncompromising or radical policy positions, while citizens mirror these patterns by aligning more firmly with partisan identities. As a result, the gap between political camps has deepened. Importantly, this pattern is not confined to the most politically informed or engaged citizens; while it is more visible in these groups, it extends to the broader electorate and shapes mass public opinion more generally. At the same time, scholars continue to debate whether polarisation originates primarily among political elites or within the mass public. Abramowitz and Saunders (2008) present evidence of ideological sorting among voters, while Fiorina and Abrams (2008) argue that most citizens remain largely centrist and that polarisation is overstated. Mason (2015), by contrast, emphasizes the growing alignment of religious, racial, and cultural identities with partisan affiliation, a phenomenon she terms identity stacking, which generates deeper affective polarisation even without corresponding increases in ideological extremity. Taken together, these perspectives suggest a dual dynamic: elites may polarise strategically to mobilize their supporters, while voters polarise affectively through identity-based attachments. Disentangling the relative importance of these mechanisms remains an open question, yet doing so is essential for designing effective policy responses.
Parallel to this debate, an important strand of research highlights the close relationship between polarisation and inequality. The idea that deeply divided societies struggle to achieve sustained growth was brought to prominence by Easterly and Levine (1997) in their study of Africa's growth tragedy, where ethnolinguistic fractionalization was found to undermine economic development despite the continents considerable potential. Building on this insight, Acemoglu and Robinson (2001) argued that wealth inequality often produces political instability, making democratic consolidation more difficult and crises more destabilizing. Their work highlighted that inequality not only shapes political outcomes but can also create fertile ground for polarisation, particularly during times of financial turmoil when the opportunity cost of unrest is low. Related contributions, such as Glaeser (2005), suggest that elites may deliberately stoke animosity and adopt extreme positions as a way of maintaining support, thereby exacerbating both polarisation and inequality.
Empirical evidence from advanced democracies reinforces this argument. In the US, McCarty et al., (2006) demonstrated that rising income inequality and partisan polarisation are closely intertwined, producing long-term shifts in legislative behaviour and political discourse. Duca and Saving (2016), using time-series analysis, confirmed the existence of bidirectional causality, showing that inequality both drives and is reinforced by polarisation. Within Europe, Pontusson and Ruenda (2008) revealed that distributive conflicts play a central role in shaping political representation. More recently, widening inequalities after the global financial crisis, coupled with the uneven effects of globalization, have fueled the rise of radical-right and Eurosceptic parties, fragmenting political systems and destabilizing established party alignments (Autor et al., 2013; Colantone and Stanig, 2018). Further studies document the spread of affective polarisation across the continent, with citizens expressing stronger hostility towards opposing parties and leaders (Reiljan et al., 2024; Wagner, 2024). The implications are clear: polarisation and inequality interact in ways that create dangerous feedback loops. Polarisation can reinforce inequality by producing policy gridlock or by entrenching biases in favor of certain groups, while inequality can fuel polarisation by sharpening identity-based divides and reducing trust in democratic institutions. This cycle is visible in numerous European cases. The Brexit referendum in the UK, the electoral realignments in France and Italy, and the rise of populist radical-right parties in Central and Eastern Europe illustrate how economic disparities can translate into entrenched political blocs and lasting institutional strains.
Despite this growing body of work, a key challenge remains how to measure polarisation in a way that is both consistent over time and comparable across countries. Much of the existing research relies on survey perceptions or context-specific indicators, raising concerns about reliability and comparability. This paper addresses that gap by employing formal measurement frameworks grounded in axiomatic principles. Specifically, we construct the first EU-wide panel of mass polarisation covering the period from 1989 to 2024, based on harmonized data from the European Election Studies (EES) Voter Study. By applying Bayesian Aldrich-McKelvey scaling to correct perceptual biases in party and self-placement data (Hare et al., 2015), and by operationalizing the Duclos-Esteban-Ray (DER) index with group decomposition, we provide a measure of polarisation that is both theoretically rigorous and empirically robust (Duclos et al., 2004).
This framework allows us to capture long-term trajectories of polarisation across Europe, identify whether polarisation arises primarily from stronger within-group identification or from widening between-group divides, and link these dynamics directly to patterns of income inequality. Our results show that polarisation intensifies as inequality widens, while the pacifying effects of growth depend crucially on the distribution of its gains. In combining formal measurement with comparative empirical analysis, this paper seeks to advance our understanding of the polarisation-inequality nexus in Europe and to contribute to broader debates about democratic stability, distributional conflict, and the risks posed by self-reinforcing equilibria of inequality and polarisation. The remainder of the paper proceeds as follows: Section 2 sets out the theoretical framework and measurement strategy; Section 3 describes the data and empirical methodology; Section 4 presents the results; and Section 5 concludes with implications for policy and future research.
