Ideological cleavages beyond the nation-state: The emergence of transnational political groups in international parliaments

Abstract

Territorial divisions are commonly believed to dominate the international realm, supposedly leaving no room for ideological distinctions to take shape. However, the formation of over fifty transnational political groups (TPGs) across thirteen international parliaments challenges this assumption, calling into question the previously accepted insignificance of ideology beyond the boundaries of the nation-state. Previously unexplored in comparative perspective, this paper investigates TPGs’ puzzling existence and delineates the conditions for their emergence within international parliaments. The theoretical argument is that homogeneity across the member states of the international parliament along three dimensions – political systems, economic development levels and geographical proximity – fosters the creation of transnational political groups. Results from regression analysis on time series cross-sectional data lend support to the theory. With the rise of international parliamentary institutions and their increased involvement in supranational decision-making over time, it becomes highly important to understand how they organize as well as the implications of their institutional designs.

1 Introduction

Political ideology is of little relevance in international governance where the main actors are nation states, and their actions are instructed by what is perceived to be the national interest. Territorial division lines allegedly structure the international realm leaving no space for functional divisions to materialize. Notwithstanding, more than fifty transnational political groups (TPGs) spanning the political spectrum have formed globally within thirteen international parliaments questioning the taken-for-granted irrelevance of ideological divisions beyond the state. This study addresses the seemingly paradoxical existence of TPGs by drawing insights from both international relations and comparative politics literatures.

The overarching theoretical argument contends that homogeneity between the member states of the international parliament is crucial for transnational political groups to develop. Rooted in cleavage theory (Rokkan, 1999; Lipset & Rokkan, 1967; Caramani, 2004, 2015), the argument goes that when the member states have similar underlying domestic cleavages, compatible ideologies are represented in the international parliament they participate in. In such a setting, the domestic conflict lines are replicated on the international level in the form of transnational political groups. Homogeneity is defined as compatibility of political regimes, economic development levels and membership geographical proximity. Conversely, if the member states face different domestic socio-economic and political circumstances, and are not coming from the same region, a territorial demarcation will remain the primary division line in the international parliament.

The theory is assessed along an institutionalist explanation that envisions transnational political groups as having less to do with ideology but simply as an institutional response to collective action problems. In line with it, political groups serve the practical purpose of reducing the transaction costs of decision-making and the easing of coalition building within a parliament (Aldrich, 1995, 2011; Cox & McCubbins, 1993). Results from a large-n analysis of more than fifty international parliaments largely support the cleavage account for TPG formation.

The exploration of transnational political groups represents a novel avenue for research, one that has been largely overlooked in existing scholarly work. With the major exception of the well-researched case of the TPGs in the European parliament (Hix et al., 2007, 2009), to date there is no comparative study on the topic. At the same time, investigating TPGs provides an opportunity to delve into the complex interplay of ideology and territory beyond nation-states, shedding light on a new facet of international cooperation and governance that has the potential to reshape our understanding of political representation and alignment on the global stage.

Examining the factors for TPG creation within international parliaments carries implications for the practice of international politics as well. The answer influences our understanding of what kind of representation international parliaments with transnational political groups can offer in comparison to traditional intergovernmental bodies. Furthermore, the presence or absence of TPGs may impact the types of norms and decisions that these parliaments are likely to promote. This could translate into different policy outcomes and international governance structures, such that reflect a broader spectrum of interests and ideologies similarly to the domestic context. Moreover, existing research suggests that transnational party groups have the potential to influence not only global politics but also national politics by molding national parties’ policy positions (Senninger et al., 2022).

The paper contributes to the emerging literature on international parliaments (Schimmelfennig et al., 2020; Winzen & Rocabert, 2021; Rocabert et al., 2019; Lenz et al., 2019). More broadly, it speaks to the body of research on the design of international institutions (e.g., Koremenos et al., 2001; Hooghe & Marks, 2015) and to the literature on global cleavages (Voeten, 2021).

Ideological cleavages are not exclusive to nation states. In fact, they determine the dimensions of competition of some international parliaments. The paper’s findings have implications for political representation beyond the state. Where transnational political groups are the result of replicated domestic cleavages, they offer citizens more effective representation, such that resonates with the functional cleavages from the home setting.

1.1 Transnational political groups in international parliaments

While International Parliamentary Institutions (IPIs) are not a new phenomenon in the international system, their proliferation has gained momentum in recent decades, with over fifty of them now in existence worldwide. (Rocabert et al., 2019; Kissling, 2011; Cofelice, 2018). Over time, some of them have expanded their competences, transitioning from consultative bodies into legislative assemblies with the capacity to impact policy outcomes (Grigorescu, 2015). Nevertheless, the majority of IPIs have limited legislative powers and their decisions are often non-binding (Schimmelfennig et al., 2020). Despite these limited legislative powers, recent research suggests that international parliaments affect global politics through influencing national positions on foreign affairs issues and on protecting the civil rights of their citizens (Koenig-Archibugi & Bareis, 2022).

During the inaugural plenary session of an international parliament, a situation akin to the initial chaos of Babylon can emerge as members of parliament (MPs) typically begin by sitting in alphabetical order. Anarchy is not a viable option, requiring them to collaborate to achieve collective action. The decision regarding how to define the assembly’s conflict lines becomes pivotal, as it can dictate the dominant actors and interests and establish the foundation for potential alliances and voting blocs. At this juncture, parliamentarians must organize their legislative work and confront a range of alternatives.

Figure 1 displays the logic of organization in 57 international parliaments.¹ The vast majority structure their everyday work based on the national delegations and design their rules of procedure accordingly. Rocabert and Winzen (2021) label such international parliaments “state-centered” because their institutional design choices give priority to the member states and their interests by following an intergovernmental logic.

Fig. 1

Organizational logic of international parliamentary institutions

Only three international parliaments resort to cross-territorial (but not ideological) logic of organization. In the Pan-African parliament, for instance, the parliamentarians regularly meet by regional caucuses (Central, East, North, South, and West Africa) and the posts within the parliament mirror that cross-territorial division (Cofelice, 2018). The Inter-parliamentary Union (IPU) - the oldest international parliament - is another peculiar case because its members form geopolitical groups.² The six geopolitical groups are vested with appreciable competencies and most of the work of the assembly is structured around them.

This study concentrates on the remaining international parliamentary institutions, which are remarkable for their propensity to forge cross-territorial alliances based on a functional rationale and structure themselves into transnational political groups.³

Thirteen international parliaments have established TPGs. While the majority of these are situated in Europe,⁴ such as the Baltic Assembly and the Benelux parliament, there are also instances in South and Central America with assemblies like Parlasur and Parlacen forming TPGs. Additionally, parliamentary bodies with membership spanning multiple regions, such as the NATO Parliamentary Assembly or the Parliamentary Assembly of the Organization for Security and Co-operation in Europe⁵ have organized into political groups. Over the last seventy years, these international parliaments have established more than fifty transnational political groups (Table A.1 in the Appendix).⁶

Figure 2 presents the emergence of transnational political groups within IPIs from 1950s to present. While there were only a few TPGs in the 1950s, their number is more than forty today. In fact, the most recent international parliament to introduce political groups was the Euro-Mediterranean Parliamentary Assembly in 2015, while the latest transnational political group to form was a radical right group that emerged in the Benelux parliament as recently as 2020.

Fig. 2

Formation of TPGs in international parliaments

The ideological composition of transnational political groups reveals which political ideologies transcend the national level and are represented in international parliaments (Fig. 3). Currently, TPGs span the entire political spectrum, encompassing six distinct ideological families. However, it’s worth noting that during the 1950s, when the first transnational political groups began to emerge in international parliaments, their ideological makeup was considerably distinct.

Fig. 3

Ideological composition of TPGs in international parliaments

Back then, only the three traditional ideological families - Christian Democrats, Socialists/Social Democrats and Liberals - had formed political groups. This is not so surprising given that these are the oldest ideologies and all of them have intrinsic transnational elements (White, 2014).

The Conservatives followed suit a decade later along with Extreme right/Nationalist TPGs. The 1970s saw the rise of extreme left and green parties and that trend was mirrored in international parliaments as well. Nowadays, five assemblies have established such groups. The political family that has spread most in recent years though comes from the opposite side of the political spectrum: while there were only two international parliaments with an Extreme right/Nationalist transnational political group in 2011, at present they are six. Regionalist parties, on the contrary, did not take root on the supranational level with the only regionalist political group in the European parliament merging with the Greens after twenty years of existence.

When the membership threshold to form a transnational political group is too high, we see some “odd marriages” between political families. For instance, in the Parliamentary Assembly of the Council of Europe the Socialists and Social Democrats Group was renamed in 2017 to Socialists, Democrats and Greens Group to reflect the incorporation of members from green parties that could not form their own political group. In other instances, even when there is a sufficient number of MPs to create an independent political group, some MPs opt to merge with a larger existing TPG as a strategic move to amplify their influence within it. This is the case in the Benelux parliament, where the right-wing Flemish nationalist party (NVA) is a part of the Christian Democrats while the green parties of the member states are in the Socialist group.⁷ With this background in place, the next section outlines the theoretical framework for the study.

2 Theoretical framework

As the best-known parliament beyond the nation-state, the European Parliament (EP) serves as a pivotal reference point for understanding the dynamics of TPG formation and ideological congruence. Existing since the inauguration of the parliament in 1950s, the transnational political groups in the EP are not superficial entities but are marked by cohesive voting behaviour that follows party lines (Hix, 2002; McElroy & Benoit, 2010). Despite the widely researched nature of the EP though, the underlying reasons for choosing ideology over nationality when the parliament was created remain obscure with extant theoretical accounts being largely tentative.

For example, historical explanations speculatively attribute the emergence of TPGs to post-WWII integration efforts to eschew nationalism (Van Oudenhove, 1965), a perspective later enriched by more “structural” interpretations (Pinder, 1991). However, the absence of a definitive theory has led scholars like Hix et al. (2003: 314) to speculate on connections between domestic party alignments and international group formation. In a similar vein, it has been argued that the expansion of transnational party politics in the European Parliament must be understood through the lens of national political parties (Hix et al., 2007).

Meanwhile, the international relations literature regards TPGs as an anomaly, and none of its existing paradigms are suitable on their own for explaining their emergence. Therefore, a good place to start looking for an answer to why these institutions exist is what we know about the emergence of political parties in the domestic context.

From the literature on party emergence within nation-states two main answers to the question “Why parties” transpire. One explanation is that political parties exist to mirror the underlying cleavages in a society by way of articulating and aggregating citizens’ demands along these cleavages (Rokkan, 1999; Lipset & Rokkan, 1967; Bartolini & Mair, 1990; Caramani, 2004, 2015). The other is that political parties emerge to resolve collective action dilemmas and to introduce more efficiency to the legislative process (Aldrich, 1995, 2011; Cox & McCubbins, 1993; Kiewiet & McCubbins, 1991). Applying these two perspectives on party formation to the context of transnational political groups, I argue for a form of the cleavage account with an emphasis on membership homogeneity.

2.1 Cleavage account for TPG formation

From a historical-sociological perspective, political parties arose in nation-states at the turn of the nineteenth century as a product of fundamental societal changes spurred by complex political and economic processes marking the transition to modernity. At the crux of these fundamental shifts were two revolutions that swept through Europe: The National and the Industrial revolutions (Lipset & Rokkan, 1967; Rokkan, 1999). These profound transformations gave rise to enduring social conflict structures – what Lipset and Rokkan (1967) call cleavages – opposing individuals, interests, and values along the cleavage lines. Each of the twin revolutions produced two cleavages: the National revolution gave impetus to centre-periphery and state-church conflicts whilst the Industrial Revolution urban-rural and labor-capital conflicts (Lipset & Rokkan, 1967). At the dawn of electoral democracy, the emerging party systems in the different European societies were a product of the mix of these four cleavages.

In every society, a myriad of conflicts pit distinct groups against each other. However, for a conflict to become a cleavage, it has to be politicized, with politicization taking the form of political mobilization and organization. Enter political parties. In line with cleavage theory, political parties emerge to mirror political cleavages and the ensuing socio-economic and cultural divisions. In a way, parties are the political manifestation of cleavages. They articulate the underlying cleavages, aggregate citizens’ demands and represent them along the fault lines. Political parties appear as instruments of self-conscious encapsulated groups with strong collective identities and solidarity towards the in-group members (Bartolini & Mair, 1990; Boix, 2009).

Building on cleavage theory (Rokkan, 1999; Lipset & Rokkan, 1967; Bartolini & Mair, 1990; Caramani, 2004, 2015) and employing it beyond the nation-state, I argue that transnational political groups emerge due to a replication of domestic cleavages on the transnational level that ensues under homogenous membership of the international parliament.

Analogously to how political cleavages advanced the emergence of national political parties, their transnational counterparts develop in cases where the underlying domestic cleavages in the member states are similar. The more the units (in this case member states instead of nation-states) are homogenous, the more divisions and conflicts crosscutting territoriality arise and find a fertile ground to develop (Lipset & Rokkan, 1967, p. 13). Membership homogeneity is theorized as compatible political regimes, economic development levels and geographical proximity.

2.1.1 Dimensions of membership homogeneity

Obviously, the international parliament’s member states can be similar or diverging on many different dimensions like population or size, to name a few. Capturing in how far the domestic cleavages of the IPI membership are homogenous and compatible though requires other characteristics come to the fore - characteristics related to the socio-economic and political structures undergirding in the respective member states.

Homogeneity is therefore conceived as member states’ compatibility along three dimensions: 1) political systems, 2) economic development levels and finally 3) membership geographical proximity (Fig. 4). Each of these dimensions and their relation to the concept of membership homogeneity are explicated in the subsections to follow.

Fig. 4

Dimensions of membership homogeneity

• 1) Political systems

The first dimension of homogeneity pertains to the degree of similarity between the political systems of the IPI member states. Simply put, when the cluster of countries constituting the IPI has homogenous political systems at the domestic level, the creation of transnational political groups is more likely. Heterogeneous political systems, on the other hand, presuppose diverging domestic political landscapes that can hardly translate into ideological divisions within the IPI. However, homogeneity in terms of political systems per se is not enough. The type of political system prevalent among the IPI membership is crucial as well since some political systems ought to be more prone to externalizing political divisions than others.

If ideological divisions are to transcend the national level in the form of TPGs, first they have to be highly institutionalized at the domestic front. Democracies tend have highly institutionalized political parties that structure the dimensions of political competition within them (Dalton et al., 2011; Dahl, 1983). Parties are an inexorable element of democracy (Stokes, 1999). Some go even as far as to claim political parties to be the “makers” of modern democracy (Schattschneider, 1942). Political parties and the ensuing ideological divisions are strongly entrenched in the political culture of democracies.

Moreover, democratic countries tend to replicate their domestic institutional settings when faced with the task of designing international organizations accordingly applying the same principles to both levels of governance (Tallberg et al., 2016; Pierson, 1996; Pevehouse, 2005). The bottom-up process of reproducing norms and practices is especially pronounced when the norm is strong and deeply rooted in the domestic institutional landscape (Grigorescu, 2015). Some version of the left-right cleavage shapes political competition in most democratic countries (Dalton et al., 2011). This holds especially for national parliaments where political conflict is determined by a functional cleavage making them the principal realm for left-right politics. Parliaments do not cater to special interests but represent pluralistically (Zürn & Walter-Drop, 2011). The strong pluralist norm in parliaments makes it likely to travel to the international level.

Consequently, democratic membership is inclined to design the founding treaties of international parliaments in a pluralistic way extending the domestic norm of pluralism. Pluralist composition means that MPs from both the parties in government and the parties in opposition become delegates to the international parliament. In this way, national parties with homogenous ideologies are represented in the assembly, giving members with a similar bent of mind the opportunity to unite in the institution of TPGs.

In settings where the membership is non-democratic, the national delegates typically are representatives from the incumbent party only. Such composition precludes an ideological alignment and fosters territorial divisions in the form of national delegations or regional blocs. The same is applicable to a scenario where the membership has heterogeneous political systems, with some member states being democratic and others non-democratic. The incompatibility of the political regimes would prevent ideological divisions to develop. Against this backdrop, the territorial logic would prevail.

• 2) Economic development levels

The second dimension capturing the concept of membership homogeneity refers to the levels of economic development across the IPI member states. International political economy literature suggests that integration is more tenable when the members of an international organization display low variance in their domestic economic institutions (Feng & Genna, 2003). Moreover, economic development is a crucial factor for what kind of cleavages and thus political parties develop within a society (Lipset, 1960). The left-right ideological dimension traditionally has a redistributive element to it (Mair, 2007) highlighting the importance of similar domestic economic contexts for the emergence of functional divisions.

Homogenous economic development across the IPI membership warrants that domestically similar socio-economic situations and challenges are present that require similar political solutions (Winzen & Rocabert, 2021).⁸ Under such circumstances, the domestic political parties are more likely to have cohesive ideologies across the member states. The resulting ideological homogeneity facilitates the organization into TPGs in the international parliament.

Contrarily, stark diversity in economic development levels across the membership implies that different social conflicts structure the political competition in the member states. Consequently, the national political parties represented in the IPI would have diverging domestic ideologies, rendering them incompatible for organizing according to a political principle. Instead, the lack of ideological cohesiveness and compatibility would likely induce territorial divisions determining the parliament’s logic of organization.

• 3) Geographical proximity (regionalism)

The last homogeneity dimension revolves around the geographical proximity of the parliament’s composition and supports the notion from regionalism theories that international institutions reflect the structures of the respective regions their membership is from (Lenz, 2018). It is further rooted in the constructivist view that collective identities play a decisive role in institution building (Reus-Smit, 1999).

Successful integration requires a sense of community (Deutsch & Burrell, 1957; Haas, 1961). Regional international organizations are more likely than cross-regional ones to exemplify some attributes of common identity based on shared history, extensive economic, cultural and political ties (Börzel, 2011). That argument naturally extends to international parliamentary institutions. Homogenous political cleavages and the ensuing ideologies (and political families) find a fertile ground to develop within a region (Caramani, 2015) rather than on the global level. Ideology encompasses various dimensions of public policy and can sustain a high degree of congruence across them. The substantive meaning of the left-right cleavage is bound to be more homogenous within a region; therefore, ideological congruence is more likely if the members of the international parliaments come from the same region.

Moreover, due to the geographical proximity, national parties from the same ideological family within a region have more interactions with each other. They learn from one other and even emulate successful policies and strategies of their counterparts in other countries (Bohmelt et al., 2016). Often, transnational links and contacts within political families predate the formation of transnational political groups (Day & Shaw, 2006; Bartolini, 2007). For example, the Socialist parties in the Nordic countries had regular transnational contacts dating back to the nineteenth century.⁹ These contacts can serve as a foundation for like-mindedness to develop. National parties within a region are therefore more likely to exemplify ideological similarity and compatibility.

Cross-regional international parliaments’ composition is more diverse. A higher degree of heterogeneity across participating states amplifies the divergence of preferences and can create a hurdle for the establishment of functional division lines. Furthermore, the more heterogeneous the member states, the less likely it is that ideological stances have the same meaning across the membership.

2.1.2 Macro-micro-macro link

While the previous section concentrated solely on the macro-level foundations of the theory, here the interplay between micro- and macro foundations is discussed unpacking the causal mechanism behind the theory and opening the “black box” characterizing the process (Coleman, 1990).

Figure 5 illustrates the theorized causal relationship between membership homogeneity and TPG establishment. Beside the macro-level foundations of the theory (dashed arrow), the mechanism accounts for the way social structures constrain individual actors (arrow 1), shape their action-formation (arrow 2), and finally specifies the process by which actors generate outcomes through their interactions (arrow 3) (Hedström & Ylikoski, 2010).

Fig. 5

Causal mechanism: Cleavage account for TPG establishment

The first arrow renders homogenous member states with compatible domestic cleavages delegating (in rare cases directly electing) MPs from the entire political spectrum to the international parliament they participate in. These MPs are coming from societies with similar social structures, societies facing similar socio-economic conditions and challenges, where similar cleavages shape the domestic political competition. At the home front, they are used to competing on ideological basis and through political parties.

Once delegated, MPs socialize with like-minded parliamentarians from sister parties in the other member states, who have kindred ideological stances, values and worldviews to their own. At the same time, their national delegation consists of colleagues from other national parties who are not adhering to the same ideology, and who might even be regarded as adversaries at home. In that sense, Socialists from one member state might have more in common with Socialists from other member states than with say Conservatives coming from their home country.

The next arrow links the actors (MPs) to their actions. As a consequence from socializing with other MPs adhering to the same ideology, like-minded MPs start organizing along political lines. Initially, organization takes the form of formal or informal meetings before the parliamentary sessions to exchange ideas, form positions and coordinate actions. Often, when MPs from one political family start organizing and forming a transnational political group, the other political families follow suit¹⁰.

The final arrow in the model shows how the (inter)actions of MPs lead to the outcome (TPG emergence). The familiarity with ideological organizational patterns from the national level translates to the international level with the establishment of transnational political groups.

Homogenous domestic social structures form the basis for ideological similarity across the parliament’s membership. This implicit ideological compatibility nudges MPs to cooperate and organize along functional instead of territorial lines culminating in the establishment of transnational political groups within international parliaments. Against this theoretical backdrop, the following hypothesis is derived:

• H1: The more homogenous the membership of the international parliament, the more likely for transnational political groups to emerge.

2.2 Institutional factors for TPG emergence

Although the macro-sociological account for party formation is a powerful explanation, Lipset and Rokkan (1967) themselves recognized that next to cleavages, institutional factors play a role in the process as well (Boix, 2009). Focusing on institutional arrangements and the incentives they generate, a rational choice institutionalist perspective on party emergence in the domestic context has less to do with cleavages, and more to do with efficiency.

According to this rational choice account, political parties emerge to facilitate the legislative work within a parliament (Cox & McCubbins, 1993; Shepsle & Weingast, 1994; Kiewiet & McCubbins, 1991). They are the institutional response to collective action problems arising from the transaction costs involved in the decision-making process (Aldrich, 1995). Political parties solve these problems by reducing the transaction costs and by easing coalition building (Aldrich, 1995, 2011; Cox & McCubbins, 1993; Riker, 1980).

Since they can attend to immense amounts of information, political parties enable efficiency through organized division of labor in a parliamentary setting (Cox & McCubbins, 1993; Schattschneider, 1942). Voting coordination and party cohesion ensues for an ideological gain since coalescing into voting blocs comes with the prospective of achieving desired policy outcomes. Moreover, coordination reduces the otherwise high dimensionality of voting making outcomes more stable and predictable (Hix et al., 2009). Conversely, in the absence of such organization chaos and uncertainty reign in the parliament.

The second set of theoretical arguments adopts this rational choice institutionalist framework and applies it beyond the domestic context to explain the emergence of transnational political groups within IPIs through its lens. Drawing on the relevant literature, I outline various institutional factors that can have an impact on the parliament’s organization below.

• 1) Number of member states

If we apply the rational choice framework to international parliamentary institutions, it is conceivable that with an increasing number of national delegations it becomes harder to ensure stable voting blocs if MPs vote along national lines. The establishment of TPGs solves the issue by making the voting and the possible alignments more predictable thus improving the chances for attaining outcomes closer to the MPs ideal points.

Additionally, a growing number of national delegations means that more conflicting views have to be accommodated in the international parliament. Cooperation then becomes strenuous. The introduction of centralized bargaining structures such as transnational political groups has the potential to remedy this problem. If the transnational political groups consolidate into identifiable voting blocs and prescribe the voting guidelines, the national delegations can manage to avoid the inconvenience of negotiating coalitions for each issue over a high volume of votes per session (Lord, 2002). With fewer members, collective action should be easier, which then allows sticking to the territorial logic. Therefore, the more member states the IPI has, the more likely for transnational political groups to emerge.

• 2) Constitutional status

Another institutional factor that could influence the formation of transnational political groups is the constitutional status of the international parliament. While the majority of IPIs are affiliated with an international organization (e.g., the European Parliament is one of the institutions of the EU), others function as independent bodies that are not embedded in a larger integration project (e.g. Inter-parliamentary Union and the Baltic Assembly). Arguably, international parliaments affiliated with an international organization are in a better position compared to the independent ones because the interaction between parliamentarians and governments is institutionalized at both the national and international levels. MPs thus dispose of more instruments to influence policies and enjoy closer contacts to administrators and politicians with high standing in the international organization (Šabič, 2008; Habegger, 2010).

Extending that reasoning, MPs can better fulfil their representation functions if there is an executive in the face of the international organization. When there is an executive to question and control, transnational ideological divisions are more likely to evolve compared to a situation where such incentives are not present (Haas & London Institute of World Affairs, 1960).

• 3) Policy scope

The policy scope of the international parliament could be relevant for the formation of transnational political groups as well. Political ideology is a relatively coherent system of values (Downs, 1957) that prescribes visions of social and political order. It is a complex system of beliefs bundling stances and preferences on a myriad of issues. Ideology is not confined to a certain policy domain; it is a heuristic introducing simplicity in a multi-dimensional decision-making setting and allowing individuals to make cognitive shortcuts (Converse, 1975). That makes it unsuitable for contexts where limited or specific issues are at stake.

Following this logic, an IPI with a limited policy scope renders the formation of transnational political groups tenuous, as the MPs would have fewer issues to find common ground on. Like-mindedness on a small number of issues might not be enough to induce a loyalty other than the national (territorial) one. The theoretical argument suggests that the more policy areas the IPI covers, the higher the probability that the diverse interests over many issues would transcend the national alignments leading up to the introduction of political groups.

• 4) Parliament’s powers

The application of democratic norms in international settings inflicts sovereignty costs for states, which in turn can become a constraint (Tallberg et al., 2014). National sovereignty concerns frequently translate into reluctance on behalf of the membership to delegate authority to supranational actors. Transnational political groups represent through the aggregation of social interests and ideological positions rather than policy expertise. The latter is the domain of the executive branch of an international organization where national interests are easier to fend (Lall, 2017). The executive follows an intergovernmental logic privileging expertise over deliberation.

The existence of TPGs augments the range of opinions and preferences, which can be problematic for the member states as functional cleavages crosscut national lines and could undermine the state interest (Winzen & Rocabert, 2021). Transnational political groups reduce the ability of states to control the alignments in the parliament by inducing a competing loyalty and representing non-territorial interests.

Such sovereignty apprehensions are justified only if the international parliamentary institution is relatively powerful, and its decisions are binding. In case the IPI does not have the power to make impactful decisions, involving enforcement and/or sanctions, the member states do not have an incentive to push their preferences on alignments in the parliament. When confronted with potential repercussions though, member states will tend to be more sensitive and try to keep the national cleavages in place where they can have maximum impact on the outcome. Accordingly, it is likely that the membership will prevent the establishment of transnational political groups in more powerful IPIs during the phase of setting up the international parliament or later on. The more powers an international parliament has, the more likely it is that the member states aspire to control the voting behavior of their delegates to ensure that the national interest is represented, in this way leaving no space for alternative alignments like a functional cleavage.

2.2.1 Macro-micro-macro link

Given the macro-level incentives stemming from the IPI institutional environment, Fig. 6 depicts the causal mechanism through which they can influence the emergence of TPGs.

Fig. 6

Causal mechanism: Institutional account for TPG establishment

In the first place, the institutional environment creates incentives that MPs have to take into account when deciding how to organize their work (arrow 1). The parliamentarians need an organizing principle and have to choose between division lines based on territoriality (national delegations, geopolitical groups etc.) and such along an ideological cleavage.

The incentives related to the number of member states in the IPI, its voting procedure, the scope of the deliberated issues, the constitutional status and finally, the powers it is vested with could sway the MPs into choosing one or the other (arrow 2). They receive feedback from the institutional environment, which shapes that decision. The model assumes that MPs will take the most rational decision given the incentives, weighing the costs and benefits associated with them. If they are better off coordinating along political lines and the labor division ensuing from organizing accordingly is associated with more benefits than costs given the institutional environment, then the decision to build TPGs appears as the optimal solution.

Finally, the institutional incentives and the cost-benefit calculations nudge them to cooperate along political lines (arrow 3). Thus, MPs react to their environment and coalesce into TPGs to facilitate their parliamentary work for pragmatic reasons. In light of these arguments, the hypothesis reads as:

• H2: The stronger the institutional incentives related to the international parliament’s number of member states, constitutional status, scope, and powers, the more likely the emergence of TPG.

It is noteworthy to briefly discuss the relationship between the cleavage and the institutional accounts. The two theoretical perspectives can either be considered as competing or as complementary to each other. If viewed as competing, the two theories offer mutually exclusive explanations: the cleavage account relies on membership homogeneity regardless of the existing institutional incentives, while the institutional perspective hinges solely on the right incentives regardless of membership characteristics. Conversely, when seen as complementary, membership homogeneity is the basic condition for TPG emergence, with institutional factors modulating the likelihood. This paper reflects the complementary approach in its empirical analysis where membership homogeneity is considered a crucial precondition that influences the emergence of TPGs. However, the theory also stresses that institutional factors contribute to shaping the organizational logic of international parliaments, thereby playing a significant role in determining the outcome.

3 Empirical analysis

The dependent variable for the analysis is the existence of transnational political groups within an international parliamentary institution. It is binary and switches to “1” in the year when a TPG (or more than one) is institutionalized for the first time. The parliaments are observed on a yearly basis also after the creation of political groups (until 2017). The rationale is that parliaments have the option to revert to another logic of alignment even after the initial adoption of ideological divisions. Such is the case in the Baltic Assembly, where political groups were established only to be dismantled later, with the assembly returning to the national delegations logic of organization.¹¹

3.1 Membership homogeneity variables

• 1. Political homogeneity

The first membership homogeneity dimension pertains to the compatibility of the domestic political systems of the parliament’s member states. The similarity of the IPI membership political systems is measured through the standard deviation of their Polity IV score (Marshall et al., 2017) over time. The original variable ranges from −10 to 10 where the threshold for a country to be considered democratic is usually “6” (Marshall et al., 2017). Low standard deviation across the member states implies that their political systems are similar whereas high scores indicate the opposite.

• 2. Economic development levels

The second dimension of membership homogeneity taps into to the countries’ economic development levels. The theory predicts that countries with similar economic development are more likely to have similar domestic cleavages, which in turn facilitates the organization into transnational political groups in the international parliament. Following Winzen and Rocabert (2020), the similarity of economic development levels across the member states is operationalized through the standard deviation of GDP per capita in thousands of USD dollars. A large standard deviation in this case indicates substantial disparities in economic development levels whereas low values point to membership homogeneity in that regard.

• 3. Geographic proximity (Regional membership)

Finally, the “regional” variable is bound to capture whether the IPI member states are coming from the same region whit the expectation that regional IPIs are more likely to opt for transnational political groups than cross-regional ones. The measure is binary and scores “0” if the international parliament has cross-regional membership, and “1” if the IPI is composed of countries from the same geographic region. The coding of the variable relies on the UN world regions classification.¹²

3.2 Institutional variables

The second set of theoretical arguments concerns the international parliaments’ institutional features, potentially influencing the organization into TPGs. The operationalization of the institutionalist arguments entails measures of the number of delegations in an IPI, its voting procedure, constitutional status, the parliament’s scope and its powers. The variables come from a time series cross-sectional data on international parliaments (ETH IPI database) (Rocabert et al., 2018; Shimmelfennig et al., 2020).

• 1. Number of member states

The functionalist argument implies that with an increasing number of member states in the parliament, it becomes challenging to build stable voting blocs. Adopting ideological divisions then reduces the transaction costs involved in the decision-making and facilitates collective action. Based on that, we should see a positive relationship between the number of member states and the existence of transnational political groups. The measure here is straightforward: the count of the IPI member states in year.

• 2. IPI scope

According to the theory, a broad range of deliberative issues in the IPI would facilitate the creation of political groups whereas parliaments with narrow scope will not prove to be a conducive environment for groups based on party logic. To measure the issue scope of international parliaments, the number of parliamentary committees is recorded over time. Committees are a good proxy to measure scope because similarly to the domestic context, in international parliaments the parliamentary work happens in the committees, and they generally correspond to the policy areas of the assembly’s competences. In that sense, the more the committees, the broader the scope of the issues deliberated in the parliament.

• 3. IO affiliation

Another theoretical expectation is that IPIs attached to international organizations are more susceptible to organizing into transnational political groups compared to independent parliaments. IPI affiliation to an international organization can take different forms. Some parliaments declare their commitment to an international organization without their affiliation being recognized by the organization (e.g., ASEAN Inter-Parliamentary Assembly is committed to the Association of Southeast Asian Nations) whereas others are recognized as affiliated institutions (e.g., Francophone Parliamentary Assembly is recognized by the Francophone Community). A third category contains international parliaments that are an integral part of the institutional landscape of the international organization (e.g., The East African Parliamentary assembly is an organ of the East African Community). To distinguish between these nuances of affiliation, a dichotomous variable encodes independent and committed IPIs with “0”, and recognized and integrated parliaments with “1”.¹³

• 4. Parliament’s powers

Lastly, a variable evaluating the decision-making competences of the IPIs captures the authority of a given parliament. The original variable from the ETH IPI database contains five levels and ranges from no powers in decision-making to sole decision-making prerogatives. To ease the model interpretation, this variable is recoded into a dummy where the first two categories of the original variable are recoded to “0”, and the other three categories into “1”. According the theory, we should see a negative relationship between IPIs powers and the existence of transnational political groups.

3.3 Results

Given the binary nature of the dependent variable, a logistic regression model is employed. The standard errors are robust and clustered by international parliament to account for heteroscedasticity and for intra-group (within-parliament) dependencies in the data.¹⁴ A time trend variable is included in the model as well.

The results reported in Table 1. In essence, the analysis lends strong support to the cleavage explanation for TPG emergence. Two out of the three variables measuring the dimensions of membership homogeneity are statistically significant and in the expected direction. On the other hand, from the rational choice variables, only the variable measuring affiliation to an international organization reaches statistical significance. The rest of the measures related to the IPI number of member states, its scope and powers remain insignificant leaving the institutional account for the existence of TPGs largely unsubstantiated.

Table 1 Logistic regression results

In line with the cleavage account for TPG emergence, the Polity IV score (SD) across the member states is negative and significant at the 5% level confirming that the more similar the political regimes of the IPI membership are, the more likely the establishment of political groups. The economic development homogeneity across the member states measured as the standard deviation of GDP per capita is also negative and significant at the 5% level. As expected, an increasing standard deviation decreases the probability of TPG establishment.

Although the results favour the cleavage explanation for TPG formation, the third dimension of membership homogeneity capturing whether the IPI is composed of states from the same region seems to bear no relevance for the formation of transnational political groups.

To gauge the marginal effects of the model estimates, the predicted probabilities of the existence of transnational political groups are plotted for all significant predictors (Figs. 7, 8 and 9).

Fig. 7

Estimated probability of TPG existence as a function of Polity IV score across the member states (Standard deviation)

Fig. 8

Estimated probability of TPG existence as a function of membership GDP per capita

Fig. 9

Estimated probability of TPG existence as a function of IO affiliation

Figure 7 reveals that when the member states of the international parliament have the same domestic political regimes (Polity IV score (SD) = 0), the predicted probability of TPG existence is very high, amounting to around 75%. Admittedly, the confidence intervals are rather wide - 30% predicted probability at the lower bound of the prediction interval and around 90% at the upper interval. Nevertheless, even by the most conservative prediction, a low standard deviation of the Polity IV score across the membership increases the predicted probabilities of TPG emergence considerably. Furthermore, a standard deviation of more than 2.5 units is associated with a sharp decrease in predicted probability of organization into transnational political groups. An even higher standard deviation makes the predicted probability to approach zero.

The following figure (Fig. 8) illustrates the influence of membership homogeneity in terms of economic development levels on the likelihood of introducing political divisions within the international parliament. A low standard deviation corresponds to an estimated probability of TPG existence of approximately 50%. Conversely, when the standard deviation exceeds 10,000 USD in GDP per capita across member states, the predicted probability for TPG existence significantly declines.

Lastly, the effect of “IO affiliation” is plotted in Fig. 9. The plot clearly shows that affiliated international parliaments have a much higher predicted probability (nearly 40%) of organizing their ranks according to political ideology compared to independent ones. Contrarily, independent parliaments are much more unlikely to form transnational political groups with a predicted probability below 10%.

In summary, the main model strongly supports the structural (cleavage) explanation for the formation of transnational political groups over the institutional one. Two out of the three dimensions of membership homogeneity appear to be decisive factors in the establishment of TPGs. Conversely, the institutional account receives less support, as only one of the four predictors appears to be a determining factor for TPG emergence.

3.4 Robustness checks

To ensure the robustness of the results, nine further models are estimated (Table A.2. below). Firstly, the argument about the compatibility of the IPI membership political systems suggests that the more institutionalized political parties are at the domestic level, the more likely their externalization within international parliaments. An alternative to the main model (Model 1 in Table 2) is estimated where instead of measuring the political systems’ homogeneity, the level of party institutionalization across the member states is measured as their mean Party Institutionalization Index score over time (Coppedge et al., 2020). The index ranges from low to high (from “0″ to “1″) and is an aggregate of several variables¹⁵ including indicators for the level of party organization (local and national); the type of party linkages to society; whether political parties have distinct from each other party platforms and finally, whether legislative party cohesion is common for the political system. The higher the score, the more institutionalized political parties are in the respective country and year.

Table 2 Robustness checks

The coefficient of the Party Institutionalization Index is positive and highly significant at the 1% level demonstrating that ideological alignments are more likely to be externalized when political parties are institutionalized at the domestic level. Additionally, the variable measuring whether the member states are coming from the same region is positive and significant in line with the cleavage account. Interestingly, the number of member states is also significant under this specification of the model. The rest of the predictors are unchanged in terms of their direction and level of significance.

The next three robustness checks employ other alternative operationalisations of some of the independent variables measuring homogeneity. First, instead of measuring the standard deviation of the member states’ political systems, the share of democracies¹⁶ within an international parliament is measured (Model 2). The new variable is positive and highly significant as expected, indicating that the larger the share of democracies within an international parliament, the more likely the creation of transnational political groups. The rest of the predictors remain robust.

Second, the mean Polity IV score across the member states is plugged into the model (Model 3). The measure is positive and highly significant lending further support to the proposition that the political systems of the member states are relevant for whether transnational political groups are institutionalized or not. The inclusion of this variable leaves the rest of the predictors unchanged.

Following Winzen and Rocabert (2020), the levels of economic homogeneity are operationalized through the kurtosis of the GDP per capita variable instead of its standard deviation (Model 4). The kurtosis of a variable accentuates the tails of its distribution and therefore such an operationalization of economic development homogeneity emphasizes the presence of outliers within an international parliament. The variable is negative as expected but does not pass the 5% significance threshold (significant at 10%).

The subsequent model examines a constructivist perspective on the diffusion of norms as an explanation for the presence of TPGs. It is conceivable that international parliaments are interconnected, and vertical diffusion processes may prompt an IPI to adopt political groups as part of its institutional framework through mechanisms such as emulation or learning from another international parliament. Qualitative evidence suggests that IPIs frequently replicate institutional designs from other organizations (Rüland & Bechle, 2014).

Within the universe of international parliaments, especially the European Parliament has the potential to act as a broker of norms and serve as a model to emulate from (Lenz & Burilkov, 2017; Biermann & Koops, 2017; Lenz et al., 2019). Investigating the institutional set-up of the Mercosur parliament, Dri (2010) suggests that the establishment of transnational political groups there might have been influenced by the extensive contacts between the EP and the Mercosur parliament.

To capture the influence the European Parliament has on other international parliaments, a binary variable is coded recording whether an international parliament has official contacts (inter-parliamentary delegations or other platforms of inter-parliamentary exchange) to the EP in a given year. Admittedly, this is by no means a perfect measure for tapping into potential diffusion effects between parliamentary institutions since the variable only records whether a given international parliament has contacts to the EP or not. Added to the original model (Model 5), the variable is not significant, and the rest of the predictors do not change in terms of direction. However, the GDP per capita (SD) and the IO affiliation variables are only significant at the 10% level. Although the diffusion explanation is not supported by the results, it needs further testing possibly through qualitative methods.

Model 6 narrows its focus to a subset of IPI cases, specifically those parliaments founded in Europe. This is due to the fact that the bulk of IPI instances that have established TPGs are found on the European continent. Except for the “regional” variable, which is omitted since all cases in this subset pertain to regional IPIs, the model retains the same variables as the main model. The findings from this analysis closely align with the results reported in the original model.

The next model presents an additional operationalization of the economic homogeneity argument (Model 7). In this robustness test, a variable was added to the main model, recording the standard deviation (SD) of the Gini coefficient across the membership of all IPIs over time. This variable draws from the Milanovic dataset “All the Ginis” (2013). While the variable is significant and aligns with the expected direction, caution should be exercised in interpreting the results from this model, as the high level of missing data in the economic inequality variable may affect the conclusions.

Arguably it is pointless to continue observing an international parliament after the adoption of transnational political groups since once created institutions become “sticky” and the dismantling of TPGs only rarely occurs. Therefore, a Cox regression with robust standard errors is estimated with the same independent variables as in the original model but only until the year when a TPG is established (Model 8). The rest of the observations (years) for that parliament are discarded. The model produces similar results as the original model, with the difference that the institutional variable measuring IO affiliation is not significant.

Model 9 introduces an alternative operationalization of the dependent variable, representing the count of TPGs in a given parliament over time, and is estimated using a negative binomial regression. While the Polity IV score maintains its statistical significance, two institutional variables become highly significant under this model specification. Specifically, the coefficient for the number of committees is positive and significant, and the powers of the international parliament appear to influence how many TPGs are created. These results align with the understanding that the number of TPGs within an international parliament would likely be more influenced by institutional incentives rather than the macro-societal characteristics of the member states of the parliament.

4 Conclusion

The global landscape is witnessing a growth in the number of international parliaments, and concurrently, their influence is expanding. Understanding the underlying logic of alignment within these institutions is crucial, as it enriches our comprehension of politics in an interconnected world. This paper endeavors to address the overarching question of the extent to which ideological divisions have taken root within international parliaments and seeks to elucidate the factors driving the emergence of transnational political groups in the first place.

The results show that transnational political groups emerge from a replication of domestic cleavages on the international level in cases where homogeneity between the member states of the parliament exists as a precondition. Their formation therefore hinges upon favourable domestic societal prerequisites, such as political and economic similarity among member states rendering their emergence to cases where such conditions are present.

These findings hold implications for political representation beyond the nation-state. Since TPGs are a reflection of domestic political conflicts and not simply institutions that ease decision-making, they can provide “citizen-centered” political representation which stands as a normatively superior alternative to the traditional “state-centered” representation (Winzen & Rocabert, 2020). Had transnational political groups been shown to arise solely due to institutional incentives, this would have implied that they are isolated from societal contexts, existing merely as practical tools. From a normative standpoint, such a conclusion would have undoubtedly diminished their capacity to provide democratic representation that extends beyond the boundaries of nation-states.

Furthermore, IPIs organized along national lines echo the intergovernmental institutional design found in the executive branches of international organizations. In that sense, international parliaments, when defined by national divisions, may confer undue legitimacy to global governance, as they do not represent the aggregated interests of individual citizens but rather perpetuate the same old intergovernmental approach. On the other hand, international parliaments featuring transnational political groups hold the potential to offer a more democratic form of political representation. This representation is designed to serve not only the interests of states but also those of citizens, based on functional cleavages rather than territorial ones.

In addition, TPGs contribute to a more political and supranational dimension in international cooperation by substituting territorial affiliations with functional alignments. These functional divisions are essential prerequisites for achieving enhanced representation and accountability (Caramani, 2015). Effectively addressing non-territorial issues necessitates alignments that transcend territorial boundaries. For international parliaments to influence outcomes as institutions, political and ideological division lines must be present, as they are key to achieving that impact. Some go even further contending that the only means for global governance to attain democratic legitimacy is to devise a supranational counterpart to national political competition through political parties (Dahl, 1999).

However, the reality remains that most international parliaments are not organized into transnational political groups and their establishment does not represent a universally applicable institutional design. It must also be acknowledged that regardless of their potential positive impact on integration and political outcomes, TPGs’ overall impact remains heavily constrained by the restricted authority vested in international parliaments. Despite these significant limitations, one can argue that with the establishment of transnational political groups international parliaments solve their inherent Babylon problem: the language of ideology presents itself as the lingua franca, the common tongue that allows their members to overcome the national differences by inducing another loyalty and a competing principal, one that they know well from their experience at home – political parties.