Development Policy under Fire? The Politicization of European External Relations
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In the past few years decision-making processes and the normative underpinnings of EU external relations have become subject to intense debate in the European institutions, member states and the wider public. Previous research suggests that there is variation in the extent to which individual domains of EU external relations are politicized and contested. This special issue aims to theorize further and investigate empirically this, using the example of European development policy and its relations with other external policies. We introduce two new mechanisms that drive politicization dynamics. We argue that politicization can be diffused horizontally from one policy field to another, which we call horizontal politicization. We also investigate how the politicization of EU external policies in third countries occurs and influences politicization dynamics in the EU, which we call outside-in politicization. The introduction to the special issue presents our theoretical approach and summarizes the key findings from the special issue.


Introduction
In the past 15 years the EU has faced many crises that have challenged the very foundations of the European integration process: the economic and financial crisis in 2007-8, the inflow of refugees and asylum seekers in 2015-16 and the 2020 Covid-19 pandemic that has resulted in the closure of European borders and spurred socio-economic inequalities. These 'polycrises' have accelerated the politicization of European integration (Zeitlin et al., 2019). Politicization is an established concept in the political sciences but also a contested one, given its various, and sometimes diverging, conceptualizations and definitions. Building on the widely accepted definition by de Wilde et al. (2016, p. 4), we refer to politicization as a three-dimensional process that includes the growing salience of debates, polarization of opinion, and an expansion of actors and audiences involved in European affairs.
Previous research has looked at the politicization of domestic policies (see Hay, 2007;Kriesi et al., 2006Kriesi et al., , 2012, the politicization of European governance and integration processes (Bressanelli et al., 2020;de Wilde et al., 2016;Hurrelmann et al., 2015) and the international level (Binder, 2013;Rixen and Zangl, 2013;Zürn et al., 2012). For a long time, EU external relations have not been on the radar screen of politicization researchers.
However, in a world that is becoming more contentious and where we see the EU striving for a stronger role in global politics, EU external relations are moving more to the fore of public political debates (Costa, 2018). In the past few years EU decision-making processes and the normative underpinnings of EU external relations have been subject to intense debates in the EP, the Council, the media and the streets (Balfour et al., 2016;Thomas, 2017). This has been visible with regard to the EU's stance in the UN Human Rights Council (Klose et al., 2017), sanctions towards Russia (Sjursen and Rosén, 2017), fisheries and trade agreements (De Bièvre et al., 2020;Young, 2016;Zimmermann, 2017), security issues (Bergmann, 2019;Hegemann and Schneckener, 2019;Wagner et al., 2017), trade policy (Gheyle and De Ville, 2017), humanitarian aid (Dany, 2015), and the EU's relations with China (Mohan, 2018). Scholars have suggested that these trends point to the increasing politicization of EU external relations (Costa, 2018;Wagner, 2017).
Despite these trends, there is little research on the politicization of EU external relations. Initial studies suggest that there is variation in the extent to which EU external policies are politicized and contested (Barbé and Morillas, 2019;Costa, 2018;Dany, 2015;Hegemann and Schneckener, 2019). These studies analyse politicization of individual fields of EU external policies in isolation. They have thereby largely overlooked the impact of increasingly blurred boundaries between different areas of EU external relations and between domestic and external policies. For example, the EU uses trade agreements to promote the Paris climate agreement and development policy to address security challenges or manage irregular migration (Leal-Arcas and Alvarez Armas, 2018; Lavenex and Kunz, 2008;Schöfberger, 2019). The adoption of the EU global strategy and its call for EU development policy 'to become more flexible and aligned with our [EU] strategic priorities' (EU, 2016, p. 48) as well as von der Leyen's new 'geopolitical' Commission underscore the EU's ambition to align development policy further with other external policies (see also Barbé and Morillas, 2019;Hadfield and Lightfoot, 2020;Olivié and Pérez, 2019). In line with previous research, we expect politicization to differ depending on the level of integration and authority transfer across specific domains of EU external policy (Costa, 2018;Zürn et al., 2012). In addition, we argue that politicization in one field can be diffused horizontally to other areas of EU external relations and politicization of the EU's policies in third countries contributes to politicization or depoliticization within the EU.
This special issue seeks to theorize and empirically investigate the politicization of EU external relations, using the case of development policy and its relations with other external policies. Development policy has often been portrayed as a technocratic, low-salience policy domain. Yet in the past couple of years there have been several indications of growing levels of conflict over European development policy. The creation of an EU Trust Fund for Africa and the diversion of aid for migration management purposes, for example, has been a matter of controversy across parliaments, civil society organizations (CSOs) and in the media (CONCORD, 2018;Rozbicka and Szent-Iványi, 2018). Populist radical right parties have contributed to increasing the salience and polarization of views on development policy. The Flemish nationalist party in Belgium, for instance, expressed resentment against EU aid by criticizing the EU's pledge of €450 million aid to help Morocco counter the coronavirus compared with the €6.5 million that Flanders receives from the EU special fund (Brozowski, 2020). Whether this anecdotal evidence of politicization reflects a broader trend in European development policy deserves further exploration, which is a main objective of this special issue.
More concretely, we seek to understand whether and how the politicization of the European development policy and its relations with other external policies occurs and unfolds. This leads to two research questions: (1) to what degree is European development policy politicized? and (2) how can the politicization of European development policy be understood in relation to dynamics in adjacent policy domains (horizontal politicization) and by the EU's external partners (outside-in politicization)? To address these questions our special issue brings together a broad variety of research covering different arenas, objects and levels of politicization as well as different policy nexuses. We have also combined various theoretical perspectives that include rationalist and constructivist approaches and different methods including statistical and discourse analyses. Building on these different approaches, we draw insights that help us to theorize the two mechanisms that may drive politicization dynamics in EU external relations and that are at the core of this special issuehorizontal politicization and outside-in politicization.
The special issue focuses on European development policy, understood as encompassing both the development policies of EU institutions and the EU's member states. As the Treaty on the Functioning of the EU defines development cooperation as a shared competence with EU member states maintaining their own development policies in parallel to the one governed by the EU institutions (TFEU Article 4.4), it is necessary to take both levels into account when analysing the politicization of European development policy. This is also reflected by the individual contributions to the special issue: some focus primarily on the politicization of the development policy of EU institutions (Chaban and Elgström, 2021;Youngs and Zihnioğlu, 2021), while others include all EU member states into their analysis (Bergmann et al., 2021;Kiratli, 2021) or opt for a selection of relevant aid donors among them (Lauwers et al., 2021;Saltnes and Thiel, 2021).
The remainder of this introductory article is structured as follows. First,we define and conceptualize politicization (section II). Second, we present findings from the individual contributions to the special issue with a focus on empirical trends in the politicization of European development policy (section III) and with a focus on how horizontal and outside-in politicization are at play in European development policy (section IV). We conclude by presenting the key contributions of the special issue and avenues for future research on politicization in EU external relations and European development policy.

I. Politicization of EU External Relations: Key Concepts
Politicization is an essentially contested concept. Against the background of various scholarly debates on its meaning, this first part of the article aims to define politicization and its main dimensions in a way that allows its use by other contributions to this volume. In doing so, we also situate the different articles of this special issue.

Defining Politicization
Scholars working on European development policy have analysed the securitization and instrumentalization of European aid for other foreign policy purposes (Furness and Gänzle, 2016;Olivié and Pérez, 2019). These analyses sometimes refer to the politicization of aid (Dany, 2015;Hilpold, 2017).
In this special issue we take a different approach, building on the conceptualization of 'politicization' advanced in EU politics and more recently in the study of EU external relations. Following Zürn (2014, p. 50), politicization means 'making collectively binding Development Policy under Fire? The Politicization of European External Relations * decisions a matter or an object of public discussion'. In addition to becoming part of public debate, an issue or a process is politicized if the polarization of opinions, interests or values takes place (de Wilde, 2011). Politicization has been understood as a discoursive phenomenon, which means that 'an issue becomes salient in political communication that seeks to influenceor responds tocollective decision making' (Hurrelmann et al., 2015, p. 45).
Hence, a widely shared view of politicization is that the concept involves a three-dimensional process of increasing salience, the polarization of opinion and the expansion of actors and audiences involved in EU issues (de Wilde et al., 2016, here and for the following). Salience refers to the attention and importance attributed to a specific issue in public or parliamentary debates or at the executive level. In our case, the term refers to how frequently and intensely European development policy is debated within the different arenas (Bergmann et al., 2021;Kiratli, 2021). Polarization refers to the scope of political conflict over an issue. Actors may hold very similar or opposing views with regard to the objectives or instruments of European development policy. Whereas development policy has traditionally been an elite affair in which a small community of decision-makers, implementing agencies and CSOs held largely similar views, we recently have observed much more opposition to development policy at the national or European level (Lauwers et al., 2021;Raunio and Wagner, 2021;or Youngs and Zihnioğlu, 2021). Finally, the term actor and audience expansionsometimes also referred to as mobilization (Rauh, 2019)signifies that a growing number of actors are engaged in the debates about European development policy. Actor expansion may also include debates travelling from one arena to anotherfor example, travelling from parliament to CSOs, or the other way around (Plank et al., 2021).
Importantly, we understand politicization as a matter of degree and a process that often unfolds over long time frames. In turn, politicization is not a dichotomous concept with clearly defined thresholds between the presence or absence of politicization, but should rather be conceived of as a gradual continuum ranging from lower to higher degrees. Moreover, we understand the three dimensions as analytically distinct, which means that, for example, an increase in salience does not necessarily lead to an increase in polarization, although in empirical reality, a change in one dimension may often go hand in hand with a change in another. In line with previous research, we will refer to the politicization of European development policy once significant changes in at least one dimension of the concept are observable, while we may speak of 'full politicization' if we have significant changes in all three dimensions (Zürn, 2016, p. 170).
Although politicization is a stand-alone concept, it has often been related to contestation, which has gained particular prominence in the literature on the role of norms in international relations (Deitelhoff and Zimmermann, 2013;Wiener, 2014;Zürn et al., 2012). In our understanding, the main conceptual difference between politicization and contestation, which has not yet been clearly spelled out in the literature, is that the former involves making something a matter of a wide public discussion that can take place in different arenas (see section 2.2.1), which is not necessarily the case for contestation, which may take place behind closed doors and within EU institutions. For example, important EU norms such as donor coordination in development policy can be contested by individual member states through their practice, without making their contestation a matter of a broad public debate (Saltnes, 2018). Hence, we argue that actors' contestation of EU norms could be an important strategy for politicization or de-politicization (as shown by Saltnes and Thiel, 2021) and can lead to increased or reduced levels of polarization (Zürn et al., 2012). However, the occurrence of contestation alone is not sufficient to diagnose (a certain degree of) politicization of a specific policy or issue.

Objects of Politicization
Having defined the main characteristics and dimensions of politicization, we need to conceptualize the objects of politicization, that is, the targets addressed by politicization processes. As de Wilde et al. (2016, p. 9) note, the literature on the politicization of European governance 'rarely distinguishes between different objects of politicization'. Nevertheless, they identify three broad categories of potential objects of politicization that can be distilled from existing scholarship on politicizationthe EU polity, EU policies and issue-specific politicization processes. While this distinction is helpful, it does not provide specific guidance on what exactly to analyse when focusing on European development policy in the context of external policies.
Thus, we propose to differentiate three potential objects of politicization processes. These objects can be politicized from within the EU or from outside: (1) objectives, that is, the goals, norms and values the EU wants to pursue with regard to development policy (for example the objective of poverty reduction) or specific elements of development policy; (2) means and instruments that the EU uses to realize its policy objectives (for example the EU Trust Fund for Africa, direct budget support or blending); and (3) partnerships, that is, the specific set of partners (such as states, international organizations, CSOs or private business actors) the EU cooperates with to achieve its development policy objectives. As the individual contributions to our special issue demonstrate, there are several objects of politicization in European development policy within these three dimensions (Table 1).

Arenas where Politicization Can Take Place
Politicization can take place in different arenas. Although the literature conceptualizes politicization in different ways, we argue that there is a consensus on distinguishing three  (Hurrelmann et al., 2015, p. 45;de Wilde et al., 2016, pp. 7-9). First, politicization can happen in institutional arenas, most notably, in parliaments, but also in any political decision-making body that allows for a certain level of public debate about a policy or an issue. Second, politicization can happen at the intermediary arena and be driven by intermediary actors such as political parties, CSOs, specific interest groups or the media. Third, politicization can happen at the citizen arena, which refers to public opinion as a locus of politicization. Research on the politicization of the European integration process has often focused on the second and third arena. The contributions to this volume demonstrate that the politicization of European development policy is observable in all three arenas, although to varying degrees ( Table 2).

Drivers of Politicization
Research that aims to explain politicization dynamics at the national and European level distinguishes between structural and actor-specific factors. Structural factors can relate, for instance, to the changing cleavages in European societies where polarization and individualization have been identified as major sources of conflict over policy objectives, instruments and desired outcomes (Costa, 2018, p. 4;Grande and Hutter, 2016, p. 22).
With the intensification of globalization new social cleavages emerge where cosmopolitans and communitarianswinners and losers of globalizationare positioned against each other (de Wilde, 2019; Zürn, 2019, p. 989). Previous research has emphasized that authority transfer (for example, in the treaty of Maastricht) and critical events (such as the Euro crisis) can trigger politicization. In development policy, for instance, the creation of trust funds as new EU instruments has increased public awareness of the relevance of the EU as an actor in addressing security and migration challenges (Lauwers et al., 2021;Montanaro and Räty, 2019;Youngs and Zihnioğlu, 2021). External shocks and critical events (Börzel and Risse, 2018;Niemann and Zaun, 2018) such as terrorist attacks in Europe, climate change emergencies, increased migration and refugee flows or budgetary scandals on the use of aid can also contribute to the politicization of European development policy. It remains to be seen whether the global Covid-19 pandemic and its health, economic, political and security-related implications, particularly for developing countries, represent another At the same time, these structural factors do not lead by themselves to politicization, but it depends on specific actors and their mobilization strategies whether authority transfer and critical events contribute to the politicization of European development policy. Previous research has highlighted the relevance of political actors and their mobilization strategies (Hutter and Grande, 2014). As the contributions to this volume illustrate (see section III), EU institutions (Youngs and Zihnioğlu, 2021), national government actors (Saltnes and Thiel, 2021), political parties (Bergmann et al., 2021;Raunio and Wagner, 2021) or CSOs (Plank et al., 2021) may take deliberate steps to increase or decrease the salience of European development policy and promote or reduce the polarization of debates on the objectives, instruments and partnerships in European development policy and increase or decrease the range of actors involved in decision-making processes. Building on these definitions of politicization and its drivers, the next two sections aggregate the key findings of the articles in the special issue on (1) the extent and degree to which European development policy is being politicized and (2) how mechanisms like horizontal and outside-in politicization are at play in European development policy.

II. Patterns of Politicization of European Development Policy
The contributions to this volume demonstrate that there are indeed many differentiated patterns of politicization of European development policy. They support our initial observation based on anecdotal evidence that development policy is becoming a matter of greater public discussion than previously. In other words, while development policy has been a rather technocratic policy field with low salience, we find overall increasing degrees of politicization. However, the patterns of politicization of European development policy vary quite significantly across the three dimensions of politicization (salience, polarization and actor expansion), with regard to the three arenas and across member states and the EU level. Also, we nowhere identify 'full' politicization, defined as significant increases of salience, polarization and mobilization (see section 2.1). In cases where some degree of politicization is found, this is often limited to one dimension. With regard to the three dimensions of politicization we discover that for some issues and in some arenas salience and polarization have increased and the number of actors involved in debating European development policy has widened, whereas in other cases little change has taken place. Kiratli (2021) demonstrates that the salience of development policy issues among EU citizens has increased since 2013. It has seen a further, gradual surge parallel to rising levels of migration into Europe. Bergmann et al. (2021) find that populist radical right parties contribute towards the salience of the migrationdevelopment nexus in light of the perceived migration crisis, but only to a moderate extent. Chaban and Elgström (2021), on the other hand, illustrate that the salience of European development policy among elites in Ukraine has been suspiciously low even though Ukraine's overall relationship with the EU has been strongly politicized. At the level of the EP, Raunio and Wagner (2021) show that the politicization of development policy has increased, but not more than in other areas of European external relations. At the same time, they illustrate how the coupling of development policy with security and immigration issues brought about polarization among political factions in the EP in  Youngs and Zihnioğlu (2021) show how polarization on EU development aid to the MENA region among EU institutions and member states has intensified significantly since 2016.
The articles in our special issue show that actor expansion is particularly relevant at the institutional level. Youngs and Zihnioğlu (2021) illustrate how the European Commission Directorate-General (DG) for migration and home affairs has taken a stronger role in defining the EU's policies towards the MENA region and Turkey.Both Raunio and Wagner (2021) and Lauwers et al. (2021) demonstrate how in the EP and some member states' parliaments populist radical right parties have started to position themselves on development policy and have contributed to politicization dynamics.
The articles show that the degree of politicization of European development policy varies across the three arenas. We see indications of growing politicization in institutional and intermediary arenas (Raunio and Wagner, 2021;Youngs and Zihnioğlu, 2021), whereas Kiratli (2021) demonstrates that the politicization of the development-migration nexus in terms of increasing salience has also occurred at the citizen level. At the same time, Saltnes and Thiel (2021) conclude that transnational coalitions between African and European CSOs contribute towards the de-politicization of support for lesbian, gay, bisexual, transgender and intersex human rights (LGBTI) rights in Uganda and argue to use a more context-sensitive approach to conditionality.
Finally, the articles in the special issue identify significant variations in patterns of politicization across EU member states. Lauwers et al. (2021) find that in the Swedish and Dutch Parliament the politicization of the migration-development nexus is high whereas in France, Italy, and others it is relatively low. Bergmann et al. (2021) show that some EU member state governments have shifted their positions on the migrationdevelopment nexus, whereas others do not see a strong link between development aid and migration at all. Saltnes and Thiel (2021) find that whereas in Sweden and the UK LGBTI conditionality is strongly politicized, in Denmark and the Netherlands it has been de-politicized over time. These fragmentary patterns suggest there are more divergences than convergences in the politicization of the aid policies of EU member states and institutions. As development policy is a shared competence, close cooperation and collective action are required if the EU and member states want to engage in global problem-solving. More divergence in aid policies and fragmented levels of politicization of development policies across the EU institutions and member states and across different arenas may make collective action even more difficult.

III. Mechanisms of Politicization in European Development Policy: Introducing Horizontal and outside-in Politicization
Building on findings from the articles in this special issue, we aim to broaden the politicization research agenda by introducing two new mechanisms: politicization dynamics that cross the boundaries of different policy fields (horizontal politicization) and politicization dynamics originating from the level of third countries (outside-in politicization). Each of these mechanisms involves a dimension of agency and structure. While elaborating on these mechanisms, this section draws from the politicization literature as well as from findings emerging from the articles in this special issue.

'Horizontal Politicization' as a Key Mechanism for Politicization
We argue that politicization can diffuse horizontally from one policy field to another and drive politicization dynamics in previously less politicized domains. According to this logic, one important explanation for politicization in one policy field would be the contagion from politicization dynamics that originally targeted another policy domain. Building on the definition of politicization presented above we conceptualize horizontal politicization as the diffusion of politicization dynamicsin terms of increasing or reducing salience, polarization or mobilizationfrom one public policy field to another.
As a basic premise, we assume that horizontal politicization is likely to travel from more politicized policy fields towards development policy. However, we do not preclude the possibility that horizontal politicization can also take the reverse direction, diffusing politicization dynamics from development policy towards other policy domains. For example, Meissner (2021) finds that the high salience of a country in EU development policy in terms of the intensity of debates on development aspects of a generalized system of preferences (GSP+) beneficiary country in the EP is an important condition for spurring debates in the EP about trade sanctions under the GSP+. Moreover, development policy actors can also use the de-politicization of development policy as a strategy in response to stronger politicization elsewhere in order to shield development policy against external influences (Lauwers et al., 2021).
Horizontal politicization dynamics do not play out in the same way for all external policy fields, but are influenced by structural and actor-specific factors. The articles in this special issue offer first insights into these enabling factors in the realm of European development policy.
In terms of structural factors, several articles point to perceived functional interdependencies between European development policy and other policy fields as enabling factor for horizontal politicization. Bergmann et al. (2021) show how populist radical right parties influence the framing of the relationship between migration policy objectives and development aid. Populist radical rights parties do not contribute only to increasing the salience of the migration-development nexus in European government programmes but also to shifting its substance towards a more restrictive approach in using development aid to curb migration patterns. This diffusion of politicization dynamics from migration to development policy is more likely the higher the vote shares of populist radical right parties (PRRPs) in previous elections and the higher their seat shares in the parliament. The findings suggest that the electoral threat and PRRPs' success at the ballot boxes puts more pressure on mainstream governments to respond to politicization pressures than PRRPs' presence in government, suggesting that mainstream's parties' perceptions of the salience of migration issues in public discourse may be an important enabling factor for horizontal politicization to occur. Kiratli (2021) finds that the inflow of refugees into the EU in 2015-16 served as a critical juncture to change public discourse about the relationship between migration and development policies and led to horizontal politicization processes at the level of public opinion. Moreover, his findings point to political interest in foreign aid issues among voters as an enabling factor for the manifestation of horizontal politicization.
Consequently, our articles indicate that if there is an established political discourse about the perceived functional interlinkages between two domains of external policy, horizontal politicization is more likely to occur.
Despite the relevance of structural factors, horizontal politicization necessarily involves agency, implying that actors take deliberate actions to link the polarization of opinions, interests or values in one policy domain to another, increase its salience or expand the actors involved in that policy field. Development policy actors can strategically use the politicization of migration, trade or climate policy to advance the salience of development aid and the range of actors involved in the field. Actors outside development policy may take deliberate steps based on cost-benefit calculations to use the politicization of their policy field to gain access to development policy resources or partnerships. Meissner (2021) finds that mainstream parties in the EP strategically contribute towards politicizing the trade-development nexus by acting upon a GSP+ beneficiary only when this country is not a EU security ally and performs poorly in terms of human development. Youngs and Zihnioğlu (2021) show how European governments and EU institutions have contrasting strategic perspectives on the instrumental use of aid in relation to migration and security policy in the MENA region and vis-à-vis Turkey. While the EP has contributed to a politicization of EU aid to Turkey in several resolutions calling for the accession process to be halted in light of the country's gradual authoritarian drift and its involvement in the Syrian conflict, the European Commission and the European External Action Service (EEAS) sought to contain a high degree of polarization within the EU and managed to convince MEPs to support a reduction in aid to Turkey without formally suspending the accession process.
Analysing actors' role in politicization processes from a constructivist perspective, Lauwers et al. (2021) conclude by suggesting that parties in government use specific discursive frames to construct the migration-development nexus in a way that legitimizes combining restrictive migration policies with traditional development aid. While PRRPs aim to politicize both migration and development policies, mainstream parties appear to construct the nexus strategically in order to de-politicize intensive European debates on migration policy.

'Outside-in Politicization' as an Additional Level and Key Mechanism for (De-) politicization
Previous research has differentiated three levels at which politicization can take placethe national, the European and the international level (Zürn et al., 2012). While these three levels have often been analysed separately, Zürn (2019) calls for more integrated perspectives to understand the interaction dynamics between the three levels. We argue that research on politicization needs to focus on a fourth level: EU partner countries. The politicization of EU policies at the level of partner countries can influence politicization dynamics in the EU, which we call outside-in politicization. This concept aims to capture the process in which the EU's policies towards a specific country are politicized at the national level of third countries, which in turn can contribute to broader politicization dynamics of European external relations. In this regard, outside-in politicization is an additional level of analysis where the EU's policies can be politicized and it is an additional mechanism that can drive politicization dynamics within the EU.
Similar to the EU's own experiences where globalization has contributed to make foreign policies a subject of intense public debate, this trend also can be observed in countries in the global South. Trade negotiations on the Economic Partnership Agreements (EPAs), for instance, have become a highly politicized issue in some African, Caribbean and Pacific countries (Hurt et al., 2013;Moerland and Weinhardt, 2020). Plank et al. (2021) find that CSOs in West Africa have contributed towards politicizing the EPA negotiations (see Moerland and Weinhardt, 2020, for a similar finding). The EU's support for the International Criminal Court has become an issue of public contestation in many African countries (Malik, 2016). The EU's LGBTI rights conditionality has been publicly and controversially debated in African countries (Saltnes and Thiel, 2021) and Ukraine (Shevtsova, 2020). Chaban and Elgström (2021) find that in Ukraine, the EU's development policy is faced with surprisingly low levels of politicization, despite an otherwise highly politicized relationship towards Europe.
Outside-in politicization can be analysed from actor-and structure-centred perspectives and through different theoretical lenses. The politicization of the EU's policies at the level of third countries could be enabled by factors not too different from politicization dynamics in Europe itself. Saltnes and Thiel (2021) show how the authority transfer hypothesis is also a relevant factor that contributes towards the politicization of the EU's political conditionality in Uganda. The EU and the EU member states' usage of conditionality to promote LGBTI rights has been perceived by Ugandan domestic actors as a breach of sovereignty and as a question of political authority. Plank et al. (2021) in their case study on the negotiations over the EU-West Africa EPAs illustrate how the transfer of competences for external trade negotiations from DG Development to DG Trade in 2001 was a critical event that led to an ambitious and persistent EU approach towards the EPA negotiations that opened up a window of opportunity for CSOs to politicize the negotiations and to criticize the negotiations' narrow focus on trade issues. CSOs then exploited the resistance to the EPAs by West African elites to further contribute to the politicization of the negotiations in the EU. Saltnes and Thiel (2021) also show how European governments in the UK and Sweden strategically depoliticize the usage of conditionality as a response to the strong politicization of European LGBTI conditionality in the case of Uganda.

Conclusions
This special issue demonstrates that there are many but differentiated patterns of politicization of European development policy across the three dimensions of politicization, arenas and across different member states and the EU level. Using the example of European development policy, we argue that politicization can diffuse horizontally from one policy field to another, which we call horizontal politicization. We also show that European external policies can be politicized at the national level of third countries and how this can influence politicization dynamics in Europe, which we define as outside-in politicization. We find that, in particular, the politicization of European migration policy but also the reactions by partners in third countries to the promotion of European norms have effects for the politicization of European development policy. Political actors have capitalized on the perceived migration crisis and have used it to reframe and construct development policy in certain ways, but the effect is moderate. In this regard, the heterogenous patterns that we find in relation to the three dimensions and arenas of politicization of European development policy are also a reflection of the fact that politicization in development policy isto a considerable extentdriven by politicization in other policy fields.
Although we have developed the concepts of horizontal politicization and outside-in politicization for the specific case of development policy and its relations with other policy fields both might be of relevance for the broader study of European external relations and politicization research.
First, by introducing the concept of horizontal politicization, we propose a conceptual framework to analyse diffusion of politicization across policy fields. This perspective does not only contribute new perspectives to politicization research. In doing so, we also conceptualize the relations between development policy and other external policy domains. Although there is a rich literature on policy nexuses, most notably with regard to the development-security nexus (Furness and Gänzle, 2016;Hout, 2010;Youngs, 2008); the development-migration nexus (Chou, 2006;Lavenex and Kunz, 2008;Schöfberger, 2019); the development-democracy nexus (Crawford, 2000;del Biondo and Orbie, 2014;Hackenesch, 2018); or the development-trade nexus (Carbone and Orbie, 2014;Elgström, 2009;Young and Peterson, 2013), this literature is relatively light in theorizing, a finding that also holds for research on European development policy more broadly (Delputte and Orbie, 2018, p. 292-293). The concept of horizontal politicization also allows us to look at these dynamics in a more open-ended way and to take into consideration reverse dynamics where, for instance, development policy influences trade, security or international climate policy.
Second, by introducing the concept of outside-in politicization we propose a framework to take into account the fact that politicization can also occur at the domestic level in third countries and thereby impact on politicization dynamics of European external policies. Investigating outside-in politicization is not only relevant in the context of European development policy where the EU's provision of aid is linked to normative objects and principles (such as good governance, the rule of law and human rights standards) and thus is not politically neutral. Moreover, the negotiation of trade and climate change agreements, EU energy or fisheries policies creates entry points for politicization in the domestic contexts of the countries concerned. The perspective of outside-in politicization broadens previous research on how external partners perceive the EU as an international actor (Chaban and Holland, 2014) as well as research on decentring EU foreign policy that questions eurocentric perspectives (Keukeleire and Lecocq, 2018).
In light of these findings, our special issue outlines three avenues for future research on politicization and on European development policy. First, this issue opens a new research perspective on the domestic politics of European development policy. Previous research has focused on the interests and power positions (and sometimes ideological orientation) of specific institutions, actors and individuals to explain policy outcomes (Koch et al., 2017;Stocke, 2019;Tingley, 2010). With the intensification of globalization and blurring of lines between domestic and foreign policies and between the different areas of European external relations, the analytical lens of politicization helps to understand and analyse the conflicts around what aid should be used for, how it should be provided and what role it should play in a broad array of foreign policies. Future research could analyse more systematically politicization processes in one arena across EU member states and the EU level, that is, the media coverage of development policy or the influence of populist radical right parties.
Second, going beyond our focus on external policies, future research could investigate whether horizontal politicization is also observable with regard to the relationship between different domestic policies, such as environmental, agriculture and energy policies. Scholarship on EU external policies could also analyse horizontal politicization in other foreign policy domains such as the climate-trade, climate-security, or the securitymigration nexus. Concerning outside-in politicization, future research could explore differences in the level of politicization of the EU's policies in the neigbhourhood compared with more distant partners and under what conditions this drives the (de-)politicization of the EU's policies.
Finally, future work should analyse the effects and broader implications of the politicization of European development policy. In the scholarly literature one finds arguments about both the positive and negative effects of politicization on EU politics (de Wilde et al., 2016;Zürn, 2014). Building on these arguments, future research questions could ask: What are the implications of politicization for the contribution of development policy to poverty reduction and global justice? If the purpose of development cooperation is indeed to pursue these objectives, why and how does it then matter whether this policy field becomes more or less politicized through its horizontal links with other policy fields or outside the EU? From a radical democratic perspective, politicization could be seen a necessary condition for enhancing emancipatory struggles, whereas the politicization of the migration-development nexus suggests that increasing politicization may not always favour an agenda for global justice.
Taken together, the insights provided by this special issue point towards a new research agenda on the politicization of European external relations.