The Evolution of Political Ideology and Polarization in Advanced Democracies: A Seat-Share and Gini-Based Analysis (1900–2023)
This investigation was inspired on Ray Dalio's concept of internal order, wherein the long-term health of a political system depends on whether factions operate within a shared institutional framework. Dalio argues that when internal conflict increases—especially when ideological factions become extreme or uncompromising—the internal order weakens, setting the stage for instability or collapse (end of an empire).
Research Question: Are we witnessing the slow erosion of the liberal democratic status quo, what might be seen as the "centrist empire" of modern democracy?
Abstract: This paper analyzes the evolution of ideological balance and polarization across advanced democracies over the last century. Using a unique dataset of parliamentary seat distributions coded by ideology, it examines long-term trends in ideological dominance, center stability, and the rise of polarization. We use a Gini coefficient framework to measure ideological dispersion and identify critical thresholds that threaten democratic stability. The findings show a stable centrist equilibrium in most democracies, with periods of fragmentation emerging in line with historical and contemporary challenges.
- Introduction
Modern democracies face recurring anxieties about polarization and democratic erosion. Classical thinkers such as Plato warned that democracies, left unchecked, drift toward tyranny or demagoguery. This study tests that premise using empirical data, assessing whether today's ideological fragmentation represents a deviation from the historical democratic norm.
We analyze parliamentary seat share data for over 35 advanced democracies from 1900 to 2023, coded by ideological families and aggregated into political blocks. Using weighted Gini coefficients and population-adjusted ideological indices, we evaluate both long-term ideological positioning and within-country fragmentation.
- Methodology
Data: Seat-share data from national parliamentary elections in advanced democracies (OECD countries), coded by ideological family (e.g., liberal, socialist, conservative, green).
Ideological Grouping: Parties are mapped to a 1–5 ideology score (1 = Far-right, 3 = Center, 5 = Far-left).
Gini Coefficient: A weighted Gini is used to measure ideological dispersion within each parliament per year.
Indexing: A global population-weighted ideology index is computed to trace average ideological lean over time.
3.1. Ideological Dominance by Family and Block Figures 1 and 2 illustrate the global evolution of ideological representation, first disaggregated by party family, then by grouped political blocks.
The data reveal that from the 1940s onward, liberal and social-democratic parties became structurally dominant in most democracies. The post-war reconstruction era solidified a model of governance in which Christian democrats and social democrats alternated power, forming the ideological backbone of modern welfare capitalism. These parties, although ideologically distinct, shared a commitment to parliamentary democracy, market economies with social safety nets, and multilateral institutions.
Throughout the Cold War, the center-left (social democrats) and center-right (Christian democrats, market liberals) captured most seats, often forming coalition governments that tempered ideological extremes. This bipartisan dominance created what some scholars refer to as the "post-war consensus" or "embedded liberalism."
Since the 1980s, however, a shift is visible: although the center remains dominant, increased fragmentation begins to emerge. This includes the rise of Green parties, regional autonomists, and right-wing populist challengers, reflecting new cleavages (climate, identity, globalization). Yet, the data confirm that the political center has endured, adapting by incorporating elements of these new demands into broad centrist platforms.
3.2. Average Ideology Over Time Figure 3 presents a population-weighted ideological index over time, with each year’s ideological midpoint calculated based on the ideological value of seated parties weighted by population.
The results are striking in their stability. From 1945 to around 1980, the average score remains firmly between 3.0 and 3.2, indicating a mildly center-left orientation. This corresponds with the global expansion of the welfare state, Keynesian economic policies, and the rise of labor-aligned parties.
In the post-Cold War era, a rightward drift becomes visible. From 1990 onward, some countries experience neoliberal realignments (e.g., New Labour in the UK, Clinton-era Democrats in the U.S.), reflected in a slight drop toward 2.8–2.9. However, these changes are modest and bounded within the central ideological corridor, suggesting that while partisan turnover increased, it did not result in a full-scale ideological rupture.
Importantly, despite recent concerns about democratic backsliding, the overall ideological center has not collapsed. Even in the 21st century, the index hovers near 2.7–3.0, showing that democratic societies have remained ideologically anchored.
3.3. Ideological Fragmentation (Gini Coefficient) Figure 4 introduces the Gini coefficient of ideological dispersion, applied to seat shares. This allows us to quantify the degree of fragmentation or concentration of ideological representation in parliaments.
Across the 20th century, Gini values generally ranged between 0.15 and 0.25, suggesting a moderate level of ideological diversity. A Gini near 0.15 implies dominance by one or two centrist parties, while values approaching 0.25 reflect multiparty systems with broader ideological representation.
However, two periods stand out:
The interwar period, particularly the late 1920s to early 1930s, shows a sharp spike in Gini values, correlating with rising fascist and communist movements, and the breakdown of centrist coalitions.
The early 21st century again shows a slow but steady rise in ideological Gini, particularly after 2008, as populist movements and radical flanks gain traction.
Notably, scholars warn that a Gini of 0.35–0.4 is critical: it suggests that roughly half the seats are held by polarized or ideologically rigid actors, impairing coalition formation, eroding policy consensus, and opening doors to democratic destabilization.
3.4. Case Study: Germany Germany offers a compelling case to illustrate how fragmentation impacts democratic resilience.
In the Weimar Republic, Gini values exceeded 0.30, rising above 0.35 by 1932–33. This reflects the erosion of the center amid growing extremism, with Nazis on the right and Communists on the left capturing large parliamentary shares. The collapse of cross-party cooperation and the eventual Enabling Act of 1933 marked the end of parliamentary democracy.
After WWII, the Federal Republic of Germany (FRG) was engineered with institutional safeguards: a 5% electoral threshold, strong federalism, and centralized party systems. The result was a dramatic decline in ideological Gini: values stayed between 0.15–0.20 throughout the Adenauer to Kohl eras.
Recent decades, however, show a modest uptick in Gini, correlated with the rise of Die Linke, AfD, and a more fragmented Bundestag. Though not (yet) alarming, this trend echoes other advanced democracies’ experiences of growing polarization.
3.5. Country Comparison: Ideological Profiles Figure 6 maps all countries by their mean ideological score and mean Gini coefficient, capturing both orientation and fragmentation.
Portugal (PRT) and Finland (FIN) emerge as left-leaning and low-polarization democracies, likely due to strong center-left traditions and disciplined party systems.
Bulgaria (BGR), Turkey (TUR), and Latvia (LVA) score as right-leaning with higher Gini values, pointing to volatile and often unstable coalitions.
Many democracies like Germany (DEU), France (FRA), Canada (CAN), and the Netherlands (NLD) cluster near ideological center with moderate Gini, representing the archetypal resilient democratic model.
This mapping shows that modern democracies have not collapsed into extreme polarization, but a significant number of cases are trending upward in Gini, warranting ongoing attention.
