Measuring factional conflict: A comparative approach using party leadership contests

Abstract

Intra-party factions have attracted increased scholarly attention in the twenty-first century as party systems have fragmented. Yet, we lack a comparative approach to identify factional conflict. We offer a novel, qualitatively derived approach to operationalize factional conflict using patterns of support in leadership contests. We apply our approach to an original dataset of 205 leadership contests from 29 parties in six consolidated democracies between 1990 and 2024. Empirically, we find that rates of factional conflict in mainstream parties increased from the first decade of the twenty-first century onwards. Niche parties had significantly less factional conflict during this period. We discuss the benefits and limitations of our approach, implications of our empirical finding, and directions for future development and application.

Keywords

faction leadership contest comparative party politics cartel party thesis mainstream and niche parties

Factional conflict¹ is a persistent feature of party politics, shaping elite coordination, party identity, and electoral performance (Bolleyer and Kölln, 2024; Giannetti and Laver, 2008; Pedersen, 2010). Factional conflict refers to the presence of competing groups within a party that hold distinct preferences about party ideology, policy, personnel, or strategy (see Klingelhöfer and Müller, 2024).² Though a vast literature has explored how parties differ from one another, fewer studies have systematically examined how they fracture internally—and how those fractures shape party behavior over time. One important obstacle to comparative analyses of intra-party politics is the lack of a consistent operationalization of factional conflict. To address this challenge, we establish and apply such a measure using a highly observable arena of factional conflict: party leadership contests.

Leadership contests offer an ideal vantage point for understanding factional conflict. As moments when competing visions of the party’s future are articulated, leadership races bring cleavages to the surface (Blum and Cowburn, 2024; Ceron, 2019). Though factional dynamics permeate many aspects of party life, conflict is most visible when factions support rival candidates, making leadership contests well-suited for comparative and longitudinal analysis.

Methodologically, we introduce a three-step approach to quantify factional conflict in parties. We first identify factions in a given party. Second, we position candidates in leadership elections as proximate to a faction based on support networks and policy positions. Third, we identify contests that are factional when leading candidates receive support from distinct factions. Our approach treats factional conflict as an emergent property of leadership contests, capturing variation over time and party. Our approach is not bound by context, timeframe, party family, or contest mechanism, and can be used to identify factional conflict in any party with leadership contests.

We demonstrate the applicability of our approach using an original dataset of 205 leadership contests in 29 parties from six consolidated democracies in the era of cartelization after 1990 (Katz and Mair, 1995, 2009). We contend that structural and systemic changes to the conduct of politics have made factional conflict more likely in the twenty-first century. We focus on the distinction between mainstream and niche parties, showing that mainstream parties exhibit increasing levels of factional conflict after 2008. Niche parties experienced factional conflict at a much lower rate during this period. Our findings suggest a more fractured party landscape than might be expected from theories about party system fragmentation alone (see e.g., Valentim and Elias, 2024), with implications for scholars’ and practitioners’ understanding of mainstream party decline. By foregrounding the role of leadership contests as a site and signal of factional conflict, this paper makes both a conceptual and empirical contribution to the study of comparative (intra-)party politics.

The challenge of studying factional conflict

Party system fragmentation, defined by the emergence of new parties into the political system, is well documented in the comparative literature (e.g., Best, 2013). Yet, the twenty-first century has also been notable for increasing fragmentation among partisan elites (Emanuele et al. 2023; Pildes, 2011) and growing intra-party affective and policy distinctions among voters (Groenendyk et al. 2020; Young and de-Wit, 2024). Theoretical scholarship on the role of party factions has enabled a more granular understanding of what is happening within the “black box” of political parties (Basedau and Köllner, 2005; Boucek, 2009). Factional conflict is also normatively important, as it influences parties’ electoral strategies, policymaking, and processes (Bolleyer and Kölln, 2024; Ceron, 2015; Pedersen, 2010). Despite these advances, there is no universally accepted approach to measure factional conflict across parties and political systems. This hinders the identification of trends, causes, and effects of factions across contexts.

Absent an agreed comparative measure, studies of factions are often limited to case studies (as noted by Kölln and Gunderson, 2024). Most empirical studies continue to rely on small-n case studies, elite interviews, or manual coding of legislative behavior. Accordingly, much of the literature remains descriptive or episodic. Quantitative analyses typically treat factional conflict as a unidimensional concept—typically ideological—overlooking the multifaceted nature of factions. Consequently, intra-party politics remains methodologically underdeveloped relative to the study of inter-party competition.

Without an understanding of how factional conflict presents in parties across political systems it is difficult to assess how institutional features structure factional conflict. The absence of a comparative measure also has practical implications for governance, as factional conflicts affect the internal dynamics of parties, influencing party unity in leadership contests and policy decisions. In extreme cases, factional conflict can result in party splits, unstable coalitions, or ineffective governance. The gap in knowledge leaves parties and policymakers ill-equipped to navigate the complexities of intra-party dynamics.

We start with an overview of definitions of intra-party factions in Table 1. Definitions vary across four main categories: organization, the degree of institutionalization a group requires to be considered a faction; cause or goals, the reason for factions existing; duration, the longevity a group requires to be considered a faction; and form(s), the sub-categories of different factional types, where specified. We also note other important features from these definitions.

Table 1.

Identifying features of party factions.

Literature	Organization	Cause/Goals	Duration	Form(s)	Other features
Key (1942, 1949)	Varies	Nomination	Any		Candidate-centered
Zariski (1960)	Some required	Patronage, strategy, policy, nomination, ideology	Any		Connection between faction and extra-party groups e.g., unions
Rose (1964)	Some required	Nomination, ideology	Durable		Membership in the legislature
Belloni and Beller (1976, 1978)	Some required	Nomination, ideology	Any
Sartori (1976)	Varies	Nomination, policy	Durable	Support or veto or policy
Reiter (1981)	Varies	Policy, ideology	Durable	Dominant or minority; realigner or regular	Groups of politicians
Polsby (1981)	Some required	Ideology, policy	Not defined	Social status concerns or not	Require a mass base
Hine (1982)	Required	Policy, patronage, nomination	Not defined	Policy differences or organizational differences	Coverage: How many faces of the party the faction is present in
Reiter (2004)	Some required	Patronage, strategy, nomination, ideology	Any: Duration downstream from cause	Kaleidoscopic or consensus or persistent
Bettcher (2005)	Required	Patronage, policy	Any	Factions of interest or factions of principle
Boucek (2009, 2010, 2012)	Some required	Ideology	Any	Cooperative or competitive or degenerative	Dynamic process rather than about identifiable features
DiSalvo (2009, 2012)	Some required	Ideology	Durable	Status quo or change; cooperative or disruptive	Party substitute
Dewan and Squintani (2016)	Defining feature	Policy	Any		Manifesto is the result of factional bargaining
Blum (2020)	Some required	Nomination, ideology	Any	Consociational or insurgent	Party substitute
Kölln and Polk (2023)	Varies	Ideology, hierarchy	Any	Ideological or hierarchical	Intra-party cleavages analogous to inter-party divisions
Cowburn (2024)	Some required	Nomination, ideology	Not defined		Organizational unit that engages extra-party groups into the party
Blum and Hans (2024)	Some required	Nomination, ideology	Not defined	Bridging or insurgent
Dilling (2024)	Organizational flexibility		Durable
Invernizzi and Prato (2025)	Not defined	Ideology, patronage	Not defined		Intra-party allocation of power

Given the continued disagreement about what constitutes a faction, we provide our definition here. Most definitions require that factions have some degree of organizational capacity, some distinct policy positions or ideological direction within the party, and some degree of temporal durability. We therefore consider factions to be organized party sub-groups with a distinct set of policy positions or ideological direction and some degree of temporal stability. This definition aligns with our previous scholarship on the topic (Blum, 2020; Blum and Cowburn, 2024; Cowburn, 2024; Cowburn and Kerr, 2023; Malpas, 2024). In doing so, we do not distinguish between the forms of factions identified in Table 1.

In conceiving of factional conflict, we extend scholarship on party (dis)unity to intra-party conflict between groups that meet our definition of factions. Following conceptual developments in a previous special issue of this journal on intra-party conflict and cohesion (Close and Gherghina, 2019; Gherghina et al. 2019), we recognize that conflict between factions may be multidimensional, such as in the distinction between substance and valence (Klingelhöfer and Müller, 2024). Similarly, our definition follows recent reflections on the term intra-party conflict (Bolleyer and Kölln 2024), requiring that disagreements must be visible to be considered conflict. Accordingly, we define factional conflict as visible disagreement between identifiable factions that include distinct policy positions or ideological differences relating to the future direction of the party.³ In short, factional conflict is intra-party conflict between factions.

By limiting our attention to conflict between identifiable factions at the national level containing substantive policy disagreements, we hope to better understand “horizontal” factional conflict as opposed to “hierarchical” intra-party competition (e.g., local branches competing with national organizations).⁴ This focus also reduces the potential for conceptual creep that allows “intra-party conflict” to include any form of disagreement within the party. Focusing solely on horizontal conflict enables a more straightforward comparison between cases because hierarchical competition is influenced by the federalization of the political system and centralization of the party organization (see e.g., Carty, 2010). Our approach is not designed to identify when parties accentuate heterogeneity as part of a broad-appeal strategy (Somer-Topcu, 2015), or where parties perceive that inconsistent messaging or strategic ambiguity may be beneficial (Bräuninger and Giger, 2018; Nasr, 2023).

Leadership contests as sites of factional conflict

Leadership contests are among the most visible sites of factional activity and therefore provide an ideal starting point to identify intra-party conflict. Leadership contests serve as “critical moments” in which internal tensions become overt (Boucek, 2009) and are commonly used in empirical analyses of factions (Blum and Hans, 2024; Ceron, 2019). Intra-party groups have strong incentives to promote an aligned member to the position of party leader to advance like-minded members, to follow a strategic approach that they perceive is better, and to pursue policy goals that members of the faction support (Ceron, 2012; Deschouwer, 2008; Harmel and Janda, 1994; Hilton, 2021). Consequently, these contests reveal cleavages within the party, with factions supporting candidates who best represent their interests (Cross and Pilet, 2015). Factional conflict in leadership selections typically occurs under standardized procedural rules and institutional constraints, making cross-case comparison easier to interpret (Pilet and Cross, 2014). Leadership contests therefore provide an empirical entry point that facilitates cross-national comparison and longitudinal analysis.

Yet, we also recognize that a focus on leadership contests cannot capture the full diversity of factional conflict in parties (see Dilling, 2024). Although our approach inevitably leaves out aspects of factional conflict (e.g., informal influence, local activism, or legislative bargaining), it provides an approach that is replicable comparatively. Our approach may also underestimate the true level of conflict if factions decided to strategically unite behind a single candidate. Yet, such a decision is also revealing about the degree of conflict if factions are willing to put differences aside. Following Blum and Cowburn (2024), we contend not that party leadership contests capture the totality of factional conflict within a party, but that other conflicts likely align with those observed in this arena.

Contemporary factional conflict in comparative perspective

Factions have gained renewed prominence in consolidated democracies on both sides of the Atlantic in the twenty-first century, where they have structured parties’ internal dynamics and influenced their ideological trajectories (DiSalvo, 2012; Kölln and Polk, 2023). Factional conflict has (re)emerged within various parties, including the US Democratic and Republican parties and the British Conservative and Labour parties (Bale, 2023; Cowburn, 2024; Minkin, 2014), reflecting a broader trend of intra-party divisions and fragmentation across Western Europe and North America in the twenty-first century. In multi-party democracies such as Germany and Spain, mainstream and niche parties alike have experienced factional conflict in recent years (Lourenço et al. 2024; Pytlas and Biehler 2023).

We therefore contend that consolidated post-industrial democracies in the twenty-first century provide an ideal setting for an initial application of our approach. We focus on the period from 1990 onward given the transformation of party organizations identified in the cartel party thesis (Katz and Mair, 1995, 2009). In the mid-1990s, Katz and Mair argued that parties in advanced democracies had entered a new organizational phase, characterized by collusion, professionalization, and state integration. Parties increasingly relied on public resources, regulated access to media, and mutually insulated themselves from electoral competition. This transformation reduced programmatic differentiation. Under these conditions, factional conflict was expected to be limited; with reduced inter-party distance in the policy space and policy being less central to political competition, conflict within parties was minimized. Parties were less sites of struggle between organized social groups, but rather semi-public agencies oriented toward collective survival. Under the cartel party model, the 1990s should therefore serve as a period of relative intra-party cohesion with low levels of factional conflict.

Yet, Katz and Mair also emphasized that the cartel party was a stage in an ongoing process of party evolution. Though cartelization might have initially resulted in low levels of factional conflict, it also changed the object of political competition. As parties became embedded in the state, access to state-aligned resources increasingly defined power within parties. This shift reoriented internal conflict away from mass representation toward control over leadership positions and institutional access. From Katz and Mair (1995, 2009), we therefore derive two phases of our empirical expectations. Initially, we envisage that parties in the 1990s, with peak cartelization, will have little factional conflict as this new organizational form stifled ideological competition both between parties and within parties. Second, we expect that the party organizational transformations associated with cartelization affected the form of future party factional conflict.

The cartel party of the 1990s is not the final form of the mass party. With increasing party system fragmentation and declining voter loyalty, cartelized parties faced internal and external pressures (Mair, 2008). This fragmentation pressured parties to accommodate potentially conflicting groups. Contemporary parties must absorb a wider array of ideological positions, strategic preferences, and—increasingly personalistic (Rahat and Sheafer, 2007)—leadership ambitions into the party tent. As parties lose status and operate in more competitive contexts, their ability to mediate internal divisions becomes strained. Electoral fragmentation may translate into factional conflict as leaders contend with shifting coalitional demands (Giannetti and Laver, 2008). The emergence and growing electoral power of new, often “extreme”, parties has introduced new accommodation incentives for mainstream parties (Meguid, 2005). In this context, factions have often sought to redefine their parties’ relationship to the state, to voters, and to emerging issues (Hopkin and Blyth, 2019). We therefore expect that party system fragmentation increases the possibility of factional conflict.

The personalization of politics exacerbates this dynamic. Under more fragmented, digitally-oriented, and candidate-centered structures, political authority attaches to individuals rather than party organizations (Karvonen, 2010; Rahat and Sheafer, 2007). Personalization incentivizes political elites to build personal brands as they compete for leadership and distance themselves from same-party opponents. We further expect that media fragmentation—defined as greater diversity in both the supply of and demand for media content in a high-choice environment (Cowburn and Knüpfer, 2024; Van Aelst et al., 2017)—accelerates this process by lowering the cost of dissent. In the digital era, factional elites can communicate directly with supporters, bypassing formal party structures and weakening the gatekeeping and disciplining functions of party elites (Knüpfer et al. 2025). The emergence of new issues in a more fragmented media ecosystem offers additional material for substantive (preference misalignment) and strategic (issue prioritization) party disagreement. It also reduces parties’ ability to ‘hide’ their differences (strategic ambiguity).

At the same time, internal party processes have become more inclusive and decentralized (Cowburn and Kerr, 2023; Hazan and Rahat, 2010), potentially exacerbating factional conflict by providing an entry point for intra-party rivals to compete. When combined with a fragmented electoral and media environment, these reforms likely further contribute to growing factional conflict. Issues that might once have been resolved through behind-the-scenes negotiations now play out in public, exposing and reinforcing factional divisions.

Following Katz and Mair (1995, 2009) as well as subsequent developments since party cartelization in the 1990s, we propose hypothesis one.

Factional conflict will increase in the twenty-first century.

Factional conflict in mainstream and niche parties

The cartel party thesis also generates expectations about which parties should experience renewed factional conflict, namely, mainstream parties. Katz and Mair focus on parties that are deeply integrated into governing the state; those that regularly form governments, structure the rules of political competition, and benefit most directly from public subventions, media regulation, and patronage. These are, by definition in post-industrial democracies, mainstream parties close to the ideological center. It is within these parties—that have been in government and are facing pressures from newly emergent niche parties—that we expect increased levels of factional conflict in the twenty-first century. Our expectation also follows from the fact that factional conflict tends to be more prevalent and policy-oriented in mainstream parties, who span more constituencies and represent more diverse interests than niche parties (Dilling, 2024; Katz and Mair, 2009), and that factions in moderate parties are the most active (Invernizzi, 2023).

Niche parties occupy a different position in cartelized party systems. They are either excluded from cartel arrangements or benefit from them indirectly, relying on ideological coherence, movement-based support, or charismatic leadership rather than access to state resources. Niche parties thus have less to gain from intra-party struggles over leadership. In cartel party terms, niche parties are challengers to the cartel rather than participants in it. Niche parties are often founded on a focused ideological identity or programmatic goal—such as Euroscepticism, environmentalism, anti-immigration sentiment, or class struggle—and are more likely to be centered around strong personalistic figures (Meguid, 2005). Whereas mainstream parties respond to shifts in public opinion in a model of “dynamic representation” (Stimson et al. 1995), niche parties are unresponsive to such shifts (Adams et al., 2006). Despite existing across the ideological and organizational spectrum, niche parties are distinct from mainstream parties in ways that matter for factional conflict.

In some situations, niche parties carry implications for factional conflict in mainstream parties (Meyer and Miller, 2015). The presence of “non-coalitionable” parties (such as the AfD in Germany) may increase internal cooperation in mainstream parties that are ideologically distant from that niche party. Conversely, non-coalitionable parties might increase factional conflict in ideologically-closer mainstream parties, with the question of whether to cooperate with the verboten party serving as a source of internal conflict. Niche parties also influence the diversity of issues on the political agenda by introducing new policies. Party system fragmentation is likely an important mechanism here; whereas mainstream parties once primarily competed with parties to their ideological center, they are now flanked on both sides. For example, center-right conservative parties once competed against center-left social democratic parties. They now find themselves competing both with their traditional rivals and with the radical right. Green and radical left parties present similar challenges to parties of the center-left.

Given our focus on supply-side politics, we use functional definitions of mainstream and niche parties (for an alternative perspective see Crulli and Albertazzi, 2024). Mainstream parties are defined by their centrality in the party system, commonly serving in the government or as the main opposition (Meguid, 2005). Conversely, niche parties are defined as “parties that compete primarily on a small number of non-economic issues” (Wagner, 2012, 845) and are distinct from mainstream parties in their positions, strategies, and perceptions among voters (Jensen and Spoon, 2010). Niche parties operate on the periphery of dominant party families, often focused on a narrower set of issues, or with the aim to disrupt established political norms and challenge the status quo (Abou-Chadi, 2016). We therefore identify mainstream and niche parties using the established rubric of party families in the literature (see e.g., Langsæther, 2023). We differentiate between mainstream parties of the ideological center—including social democratic, Christian democratic, conservative, and liberal parties—and niche parties on the periphery, including radical left, radical right, green, and regional parties.⁵

The increase in factional conflict in the twenty-first century will occur in mainstream parties of the ideological center, rather than in niche parties from ideological poles.

Data scope

We apply our approach to parties in six consolidated democracies that vary across the systemic features that influence factional conflict. Given our expectations, we collect data about leadership contests in Canada, France, Germany, Spain, the United Kingdom (UK), and the United States (US) across the 35 year period between 1990 and 2024.

As outlined above, we expect that factional conflict became more prevalent in the twenty-first century relative to the 1990s. We recognize that issues in the 1970s and 1980s—including but not limited to nuclear disarmament, relationships with the Soviet Union, and the privatization of public services—may mean that levels of factional conflict were higher in these earlier decades. Focusing on this later period allows us to test our argument that cartel parties had comparatively low levels of factional conflict in the 1990s, with an emergent form of factional conflict in the twenty-first century. Our claim is not therefore that factional conflict was less prevalent in decades before the 1990s, but that its later form is qualitatively distinct from eras of mass-party factional conflict. Studying factional conflict before and during this period would be a comparison of different organizational logics (Katz and Mair, 1995).

In Table 2, we show how these countries differ in their governmental systems, degree of centralization, electoral systems, positions of the executive, method of party financing, ages of democracy, and formal roles of factions in the legislature. Extant scholarship identifies these factors as structuring the degree of factional conflict within parties; we summarize this literature in the supplemental material. Given the institutional differences between these countries, we contend that identifying consistent patterns of factional conflict suggests that these trends are not the result of any one feature. In short, our cases are diverse in the ways that matter for factional conflict.

Table 2.

Summary of political systems.

	Canada	France	Germany	Spain	UK	USA
Degree of centralization	Federal	Centralized	Federal	Devolved	Devolved	Federal
Electoral system	Plurality: FPTP	Majoritarian: Two-round runoff	Mixed: FPTP & PR	Proportional: PR⁶	Plurality: FPTP	Plurality: FPTP
Party system (Effective # of parties, year last available)	Two + party system: (2.76, 2021)	Multi-party system (3.72, 2022)	Multi-party system (5.51, 2021)	Multi-party system (3.44, 2023)	Two-party system (2.39, 2024)	Two-party system (2.00, 2022)
Position of the executive	Within the legislature	Independently elected	Within the legislature	Within the legislature	Within the legislature	Independently elected
Party finance	Public & private	Public & private	Public	Public & private	Public & private	Private
Age of democracy	Old	Old	Medium	Young	Old	Old
Formal legislative factions	No	No	Yes	No	Yes	Yes

We think there is particular merit in comparing North American and Western European democracies. US parties are often seen by political scientists as “exceptional,” a dynamic furthered by the siloing of scholarship between “Americanists” and “comparativists” in the US. Despite the US’s supposedly exceptional status, parties across consolidated democracies face similar threats and challenges in the twenty-first century. Yet, a disproportionate share of party politics research focuses on the US, with limited transatlantic exchange on the topic of intra-party politics. The comparison of North American and Western European countries therefore reflects both the common challenges of fragmentation in the twenty-first century and our normative position that scholars working on these topics on both sides of the Atlantic have much to gain through collaboration.

We include all national parties that gained substantive representation in the national legislature, as well as some prominent regional parties. The list of 29 parties is shown in Table 3. What constitutes party leadership varies between countries; we detail our inclusion criteria in the supplemental material.

Table 3.

Parties included.

Country	Parties
Canada	Conservative Party, Liberal Party, New Democratic Party (NDP), Bloc Québécois
France	Rassemblement pour la République (RPR), Union pour un Mouvement Populaire (UMP), Les Républicains (LR), Parti Socialiste (PS), Renaissance (RE), Rassemblement National (RN), Union pour la Démocratie Française (UDF)
Germany	Christlich Demokratische Union Deutschlands/Christlich-Soziale Union Bayern (CDU/CSU), Sozialdemokratische Partei Deutschlands (SPD), Alliance 90/Die Grünen, Freie Demokratische Partei (FDP), die Linke, Alternative für Deutschland (AfD)
Spain	Partido Socialista Obrero Español (PSOE), Partido Popular (PP), Ciudadanos, Vox, Podemos, Sumar
UK	Conservative Party, Labour Party, Liberal Democrats, Scottish Nationalist Party (SNP)
USA	Democratic Party, Republican Party

Measurement

We take a three-step approach to identify factional conflict in party leadership contests. We first identify factions within each party using a combination of extant literature, accumulated individual case knowledge, and news coverage.⁷ We present each party’s factions and identifying characteristics in the supplemental material. This qualitative approach ensures contextual understanding of the nature of intra-party politics and is time and knowledge intensive. Yet, developing an understanding of particular factions in parties using these sources is possible across cases.

Second, we collected data on candidates in leadership contests. For each candidate, we identified which faction they aligned with or received support from, if any. Being aligned with a faction included receiving formal support from organizations associated with a faction, for example Momentum in the British Labour Party. It also included receiving support or an endorsement from prominent figures in a faction; for example, Jeremy Corbyn or Björn Höcke. We also identified alignment through congruence between campaign policy positions and stated positions of factional leaders or organizations within the parties. For example, supporting Medicare-For-All or the Green New Deal in the US Democratic Party or the Hartz IV reforms in the German SPD (see Cowburn and Kerr, 2023). Most candidates were identifiable as aligned with or having support from a particular faction in their party, producing a dataset of all candidates in party leadership contests with their factional alignment.

Third, we coded whether the leadership contest can be considered ‘factional’. We code contests as factional (1) when the two highest-placed candidates received support from distinct factions in the party. When these candidates do not come from distinct factions, we code contests as ‘non-factional’ (0). At least two candidates must stand in a leadership contest for the contest to be classified as factional.⁸ More than one candidate standing (“a contested leadership election”) is therefore a necessary but not sufficient condition for a leadership contest to be considered factional; all factional contests are contested but not all contested leadership elections are factional. The most visible way of signaling the lack of conflict is uniting behind a single candidate in an uncontested leadership election.

We illustrate the distinction between contested and factional leadership contests in the British Conservative Party. The 1995 leadership challenge by John Redwood was widely understood as an expression of no confidence in John Major’s ability to lead the party and country, and is not coded as factional in our data, despite being contested. The July to September 2022 contest between Liz Truss and Rishi Sunak focused on policy differences, most notably on the economy, with each candidate receiving support from distinct groups within the party based on these positions, and is therefore coded as factional. The October 2022 leadership “contest” where Rishi Sunak stood unopposed was not contested and, by extension, not factional.

Empirical application

In hypothesis one (H1), we expect that, for all parties, we should observe an increase in factional conflict in the twenty-first century. Figure 1 shows the rolling average of factional conflict in all parties across each 4-year period⁹ with 95% confidence intervals and local mean smoothing to identify underlying trends, depicting temporal variation while adjusting for short-term fluctuations and uncertainty in the data. Though there is a slight decline from 1990 to 2008 and a slight increase from 2008 to 2024, these trends are not statistically significant, indicating that, at the aggregate level, parties did not become significantly more factional in the twenty-first century. We do not find support for H1.

Figure 1.

Factional conflict (all parties).

We present our temporal trends grouped into mainstream and niche parties (H2) in Figure 2. We identify little difference between the groups in the 1990s and 2008, with slight (non-significant) downward trends in both groups. After 2008, mainstream parties became significantly more factional, with around 30 percent of contests being factional in 2008 compared to more than half of contests being factional in 2024. In contrast, though niche parties became slightly less factional, this difference was not statistically significant. The post-2008 increase in factional conflict shown in Figure 1 is concentrated in mainstream parties. Whereas rates of factional conflict in mainstream and niche parties were once indistinguishable, mainstream parties now have factional leadership contests at a significantly higher rate.¹⁰ This finding supports H2.

Figure 2.

Factional conflict (mainstream vs niche parties).

Empirical discussion

Our temporal analysis in H1 indicates a slight decline in factional conflict from 1990 until 2008, followed by a rise in line with our expectations, but these differences are not statistically significant. When we separate mainstream and niche parties, we find that factional conflict became significantly more common in mainstream parties from 2008 onwards, producing a difference in the level of conflict in mainstream and niche parties in this period.

In line with our expectations about factional conflict in mainstream and niche parties in an era of cartelization, we see two clear stages with an inflection point in 2008. We expected that, in the 1990s, cartelization would reduce levels of factional conflict for mainstream parties, which would then increase in the twenty-first century. One potential explanation for increasing conflict in mainstream parties is that as cartelization matures, factional groups begin to compete for access to state resources. We did not explicitly state any dynamic expectations for niche parties, though we see somewhat lower levels of factional conflict over time.

Global “crises” around 2008—including but not limited to the global financial collapse, an upsurge in immigration, growing effects of climate change, and reforms that weakened party authority—might have induced factional conflict in mainstream parties who struggled over how to confront a changing world. We further suspect that the changing media ecosystem, with a shift towards digital platforms that enable individual politicians to bypass traditional party structures and communicate directly to voters, might have served to both fragment mainstream parties and to unify personalistic niche parties around “charismatic” figures (see e.g., Cowburn et al. 2025). To help understand the relative importance of global factors versus the institutional features of political systems, we present the trends by country and party family in the supplemental material.¹¹

Conclusion

We offer a novel approach to identify factional conflict using leadership contests. We then demonstrate the utility of this approach by applying it to parties in six consolidated democracies across a 35 year period of party cartelization. We find evidence of an increase in factional conflict in mainstream parties from 2008 onwards.

Methodologically, our approach enables researchers to compare levels of factional conflict across time and context. Our approach builds factional maps based on elite alignment during leadership contests. Because it is rooted in observable behaviors, our approach allows for dynamic cross-national comparison. This approach might serve to normalize factional conflict in parties, which continues to have negative connotations—not least in the US, with cautioning against the “mischiefs of faction” (Madison, 1787)—potentially shaping both public discourse and empirical scholarship on the phenomenon.

One limitation of our approach is our sole focus on party leadership contests (Bentancur et al. 2019; Dilling, 2024). In recent years, the subject of candidate selection has become increasingly contested in a range of parties, serving both as a site of factional conflict and as a tool for wielding power over the party (Cowburn and Kerr, 2023; Hazan and Rahat, 2010). One obvious extension of our approach is to look beyond leadership contests to study factional conflict around the process of candidate selection. Second, the need for case-level knowledge may limit the scalability of our approach. Scholars working across cases without established literatures may find it difficult to identify factions. In these contexts, our approach may require supplementation with elite interviews, archival work, or long-term observation.

Our empirical findings reveal the degree of factional conflict in a comparative setting. The emergence of different levels of factional conflict between mainstream and niche parties aligns temporally with struggles that parties of the political center have experienced in recent decades.¹² We find comparatively low factional conflict during peak party cartelization in the 1990s and early 2000s (Katz and Mair, 1995, 2009). Since 2008, political and ideological contestation has reemerged within mainstream parties and factional conflict rose. As these parties attempted to manage broad coalitions under conditions of ideological fragmentation, shifting electoral alignments, and declining partisan loyalty, leadership contests have become important venues for internal renegotiation. In these moments, factions have become vehicles for party adaptation and realignment (Blum and Hans, 2024; DiSalvo 2012).

Establishing causal connections between challenges to parties and factional conflict is an area for further research. Internally, reforms intended to enhance intra-party democracy may lower the costs of mobilizing for factional conflicts. Externally, parties operate in an increasingly volatile environment shaped by global economic crises, cultural and geopolitical shocks, and a rapidly evolving issue space that introduces new, often cross-cutting, lines of conflict. Meanwhile, fragmented digital media ecosystems reduce the capacity of party organizations to manage dissent privately, enabling factional actors to bypass traditional gatekeepers by appealing directly to supporters using ideologically-supportive media (Knüpfer et al. 2025). Understanding how internal organizational reforms interact with external systemic pressures to produce factional conflict is another avenue for work on intra-party politics. Similarly, future scholarship might extend this approach to examine how different factional forms—of interests, of principles, or candidate-centered—result from or exacerbate these dynamics.

The recent rise in mainstream factional conflict may also have implications for democracies. Whether factional conflicts strengthen (The Benefits of Conflict, 2022) or weaken (McGann, 2002; Snyder and Ting, 2002) parties electorally remains debated. Comparative research still also has little to say on the relationship between factional conflict and the outcomes of the legislative process, either in terms of efficiency (Volden and Wiseman, 2014) or design (Hurka et al., 2025). Our approach can be used to study the consequences of factional conflict for electoral performance, legislative efficiency, and legislative design.

The divergence between mainstream and niche parties in patterns of factional conflict invites reflection on the organizational resilience of parties. Niche parties, often organized around singular ideological principles or “charismatic” leaders, appear better insulated from rising contestation, at least in the context of leadership selection, suggesting trade-offs between cohesion and inclusiveness, where the centralization of authority in niche parties might insulate them from the instability affecting mainstream parties. Such questions offer fertile ground for future work on party institutionalization, elite coordination, and the position of party families.

Supplemental material

Supplemental Material - Measuring factional conflict: A comparative approach using party leadership contests

Supplemental Material for Measuring factional conflict: A comparative approach using party leadership contests by Mike Cowburn, Amelia Malpas, Rachel M. Blum in Party Politics

Footnotes

Acknowledgements

We thank participants of the 2024 APSA panel and the 2025 EPSA panel on intra-party politics. In particular, we thank Matthias Kaltenegger, Jacob Gundersson, Ann-Kristin Kölln, and Steffen Hurka for their helpful comments on various aspects of this project. We are grateful to research assistants Christoph Rosa and Felix Trojan.

Declaration of conflicting interests

The authors declare no conflicting interests in this project.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

ORCID iD

Mike Cowburn

Supplemental material

Supplemental material for this article is available online.

Notes

Author biographies

Mike Cowburn is a Research Fellow in the Department of Political and Social Science at Zeppelin University in Friedrichshafen where he works on the ERC-funded project DEMOLAW examining the design, creation, and survival of democratic laws in the US, UK, and EU. His research interests include intra-party factions, candidate nomination, legislative politics, and political communication. Mike’s first book, Party Transformation in Congressional Primaries: Faction and Ideology in the Twenty-First Century (Cambridge University Press, 2024), examines how intra-party competition has contributed to party change in the twenty-first century by looking at the nomination process for candidates to the U.S. legislature. He received his Ph.D. from the Freie Universität Berlin in 2022.

Amelia Malpas is a Government Ph.D. student at Harvard University. Her research focuses on political parties with special attention to factional or other group conflict within party coalitions over distributional issues.

Dr. Rachel M. Blum is Associate Professor at the University of Oklahoma, where she holds appointments in the Department of Political Science and the Carl Albert Congressional Research and Studies Center. Dr. Blum’s scholarship focuses on political parties and party factions. She is the author of multiple peer-reviewed publications, including the books How the Tea Party Captured the GOP: Insurgent Factions in American Politics (University of Chicago Press, 2020) and Cooperating Party Factions: A Network Analysis of Party Divisions in U.S. Presidential Nominations (Cambridge University Press, 2024). She received her Ph.D. in 2016 from Georgetown University.

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