How much do the prospects of international recognition of a possible new state affect the domestic support for secession? To answer this research question, we adopted a most similar systems design and conducted a Web‐based survey experiment in Catalonia and Scotland. Respondents were presented with plausible scenarios regarding the international recognition of a hypothetical independent state by other countries and were subsequently asked whether they would support a unilateral declaration of independence. The results show that the prospects of international recognition as a sovereign and independent state influence the degree of support for a unilateral declaration of independence in both cases. This effect was moderated by the intensity of nationalist sentiment and the motivations for independence. Respondents with more outspoken nationalist sentiments were only marginally influenced by these scenarios or treatments. Moreover, participants whose preferences towards secession were driven by ethno‐political motivations were less influenced by international factors than those who wanted an independent state for economic or political reasons.

I do not want to be the President of Freedonia. I refuse to walk around the world, handing out business cards of a Republic that does not exist. Catalan President Carles Puigdemont during a cabinet meeting discussing a possible unilateral declaration of independence in October 2017 ( García, 2018, p. 216)

1 INTRODUCTION On 27 October 2017, the Catalan Parliament adopted a resolution to unilaterally declare Catalonia's independence from Spain and the foundation of a Catalan Republic. As the quote above illustrates, the regional premier feared that an independent Catalonia would lack international recognition and thus be analogous to the fictitious country of Freedonia, as in the Marx Brothers' movie Duck Soup. President Puigdemont's apprehension of Catalonia becoming a small and isolated Freedonia was justified, given the messages conveyed by the international community. The President of the European Parliament Antonio Tajani made clear that “no one in the European Union will recognise this declaration,” whereas the US State Department affirmed that “Catalonia is an integral part of Spain, and the United States supports the Spanish government's constitutional measures to keep Spain strong and united” (Tajani, 2017; US State Department, 2017). Most political parties favouring a secession from Spain had assumed that gaining independence would go hand in hand with retaining or acquiring EU membership, but Brussels was quick to signal its lack of appetite for new enlargements, whether “external” or “internal” (Closa, 2016, pp. 243–244). On the day of the unilateral declaration of independence, the Spanish Government imposed temporary direct rule over the Autonomous Community of Catalonia and called for fresh elections. Four days later, the declaration was fully suspended by the Spanish Constitutional Court, and various members of the Catalan government had either fled the country or were awaiting legal prosecution for rebellion, sedition, disobedience, and embezzlement of public money. Various accounts and political analyses of the “Catalan process” highlight the lack of international support and the difficulty in combining secession and immediate EU accession as some of the key reasons for the regional government's reluctance to proceed with its unilateral agenda (Muro, 2018; García, 2018, pp. 215, 240). The above‐mentioned episode illustrates that the Catalan secessionist process was not a purely internal issue but a phenomenon with both domestic and international dimensions. Indeed, the formation of new states is usually preceded by a domestic push for separation, but their full recognition depends on the will of consolidated states to acknowledge the existence of the newcomer. Scholarly research has discussed how international factors influence the dynamics of secessionism and the emergence of new states (Coggins, 2011; Cunningham & Sawyer, 2017; Fazal & Griffiths, 2014; Griffiths & Muro, 2020). These studies have identified the factors and mechanisms that explain why foreign powers may support secessionist movements and why some states gain international recognition—the latter widely seen as one of the key features of a sovereign state (Coggins, 2011; Fabry, 2010; Fazal & Griffiths, 2014)—while others stay in the limbo of being a “contested state,” namely, an entity lacking international recognition of its status as an independent state. Little scholarly attention, however, has been devoted to the question of how international recognition may affect domestic support for secessionist movements. While most studies approach secessionist movements as units of analysis, the attitudes of the general population that make up the contested nations have been conspicuously absent. One notable exception is provided by the work of Nadav G. Shelef and Yael Zeira on the impact of the United Nations General Assembly's (UNGA) 2012 recognition of Palestine on mass attitudes towards a two‐state solution (Shelef & Zeira, 2015). Their work used a combination of panel data and a survey experiment to make the argument that international recognition by the UNGA‐shaped Palestinian attitudes towards territorial compromise in two ways: International recognition simultaneously increased support for partition as a strategy of conflict resolution as well as decreasing support for compromise on the territorial terms of partition. However, “who” was specifically influenced by international signals and “why” they were influenced by them were questions that remained largely unanswered in the paper. In similar fashion, Muro and Vlaskamp (2016) explored how the perspectives of European Union (EU) membership influenced the microfoundations of support for independence in Scotland and Catalonia. Their study measured the impact of positive and negative information treatments on the prospects of EU membership and concluded that positive incentives changed support for independence, whereas threats and sanctions produced null effects, especially in the Scottish case. Their research design did not take into account the fact that, in contrast to Spain's opposition to Catalonia holding an independence referendum, the UK adopted a more accommodating position, making the threat about EU exclusion less credible. The British government's strategic calculation had been that the Scottish referendum was a low‐risk option, given that opinion polls suggested that only 30% of the Scottish public supported independence. The vote on independence was thus seen as an opportunity to deliver a substantial defeat for the ruling SNP, strengthen the democratic credentials of the UK, and annihilate demand for independence for a generation. The strategy clearly backfired and future governments are likely to adopt a more restrictive position, given that both the Scottish and Brexit referendums proved to be high‐risk strategies for the incumbent party. Following the UK's probable departure from the EU in 2019, the Conservative and Labour parties may find new electoral incentives to oppose a second Scottish referendum and argue that “now is not the time” (Cetrà & Harvey, 2018, p. 8). As in the case of the failed Catalan Republic, nationalist leaders may be tempted to declare independence unilaterally if they believe that an agreed secession with the host state is not feasible in the short term and that there is sufficient domestic support for a new sovereign state. Needless to say, not all supporters of secession may be willing to assume the political and economic risks of unilateral decisions and may prefer long‐term bilateral agreements. This paper contributes to the existing literature on secession by studying the extent to which the prospects of international recognition of the entity as a new state (or the lack thereof) influence popular support for a unilateral declaration of independence. In other words, it examines the extent to which individuals feel supported or restrained from taking this leap in the dark by international factors. By using data from a Web‐based survey experiment including 2,400 participants interviewed in Catalonia and Scotland, we show the effect of international threats and incentives on preferences for secession, especially among individuals with mixed national and regional identities. The results clearly suggest that the prospects of international recognition influenced popular support for a unilateral declaration of independence in both cases. However, the effects of these credible scenarios for and against independence were not homogeneously distributed and were moderated by the individual's degree of nationalist sentiment. First of all, the more nationalist participants were only marginally influenced by the hypothetical situations (or treatments). Second, respondents whose preference for an independent state were driven by ethno‐political motivations were less influenced by international factors than respondents who favoured secession for economic or political reasons. In other words, different types of people were influenced differently, which improved our knowledge of the conditions under which international threats and sanctions work. The article is structured as follows: First, we discuss the relationship between domestic support for secession and international recognition and introduce the four hypotheses to be tested. Second, we describe the online survey experiment and justify the rationale for case selection, which adopts a Most Similar Systems Design. Third, we present the results of the experiment and discuss the role of international incentives on social and political demands for self‐determination. We finally summarise the findings and discuss their policy implications.

2 INTERNATIONAL RECOGNITION AND DOMESTIC SUPPORT FOR SECESSION Secession is understood as a “process of withdrawal of a territory and its population from an existing state and the creation of a new state on that territory” (Radan & Pavkovic, 2011, p. 1). For new states, the easiest route to obtaining international recognition is to secede with the permission of the former metropole or central government. Once the former host state recognises the new state, the rest of the international community usually follows rather quickly. In the recent past, such mutually agreed secessions were usually preceded by a referendum in which the population voted its preference (e.g., in Montenegro or South Sudan). However, such a scenario is more the exception than the rule, and in most cases, the metropole is vehemently opposed to secession for reasons such as emotional attachment, fear of a snowball effect, a sense of injustice, or economic motives (Coggins, 2011; Griffiths, 2016; Ker‐Lindsay, 2012; Sterio, 2012). If the host state does not recognise the act of secession and the constitution of a new state, we can speak of a unilateral secession. Historically, only about half of the world's new states had the former home state's consent to secede (Coggins, 2011, p. 446). In these cases of unilateral secession, there can be a discrepancy between “de jure” and “de facto” states, depending on whether the state legally exists, regardless of the practical situation on the ground, or exists in reality but lacks recognition by other states. Since the end of World War II, de facto and juridical sovereignty have been clearly decoupled, something that has caused the emergence of so‐called “contested states” lacking international recognition, for example, Abkhazia, South Ossetia, Somaliland, or Northern Cyprus (Fabry, 2010; Florea, 2014). Most former host states use all tools at their disposal (from diplomacy to war) to prevent the broader recognition of these contested states. In some cases, the hope is that the secession can still be undone, as was the case with Katanga (Zaire, present‐day Democratic Republic of the Congo), the Confederate States of America, or the short‐lived Catalan Republic. In other cases, promoting the international isolation of the new state is a tool of retaliation or a way to force the new state's government to renegotiate the terms of secession in a more orderly manner (Ker‐Lindsay, 2012, p. 70ff). In the eyes of both proponents and opponents of secession, international recognition is a unilateral political act taken by another country or international institution, which affects the domestic support for political independence. The hypotheses guiding this paper are concerned with the research question of how the prospects of international recognition influence individuals' political attitudes towards unilateral secession. Since neither the Scottish referendum nor the “Catalan process” have settled the territorial issue, the possibility that any of these two stateless nations (or any other region of an EU state) might initiate new bids towards secession in the future cannot be ruled out. Independence referendums will continue to be rare events in advanced industrial democracies, but this will not discourage secessionist movements from initiating similar bids towards independence (McEwen & Keating, 2017). Movements in favour of remedial secession will likely ponder over the costs and benefits of unilateral actions, while keeping a close eye on the preferences of big powers. Thus, the first and second hypotheses sought to test whether the prospects of international recognition would have an effect on support for a process of secession that was not negotiated with the host state: H1.The prospect of international recognition will have a positive effect on support for a unilateral declaration of independence. H2.The prospect of lacking international recognition will have a negative effect on support for a unilateral declaration of independence. The rationale for these hypotheses is that domestic audiences might perceive international support as an indicator of the feasibility of the unilateral separatist project, hence making a positive contribution to the cause. Under conditions of uncertainty, political support of great powers (or the absence of it) can make or break new states. As suggested by Sterio, we understand the five permanent members of the UN Security Council (the United States, Russia, China, France, and the UK), three of the four remaining G8 members (Germany, Italy, and Japan) and India as Great Powers (Sterio, 2012, p. 44ff). While support and recognition of individual states can keep “contested states” economically alive (e.g., Turkey's support of Northern Cyprus), it may not be enough to provide unrecognised states with the necessary financial capabilities to serve their populations effectively and act as responsible members of the international community. Support from great powers is important, as “their recognition carries the greatest weight and has the greatest potential influence on others. Typically early movers, the decision of great powers to acknowledge a new state serves as a focal point that initiates a cascade of legitimacy throughout the system's remaining members” (Coggins, 2011, p. 449). Major powers may also apply pressure on the host state to recognise the new state (Paquin, 2010), especially in cases of “remedial secession,” where there is systematic oppression or exploitation. For example, due to domestic anticolonial sentiments and geostrategic considerations, in 1949, the United States threatened the Netherlands with exclusion from the Marshall Plan if it did not accept Indonesia's independence (Kromhout, 2001). Furthermore, as Saideman points out, “secessionist movements that gain recognition can join international organizations, get finances from regional and world financial institutions and generally join the club of countries. Those that do not get diplomatic recognition dwell in an ambiguous situation where informal economic exchanges tend to predominate” (Saideman, 2011, p. 267). Especially for small states, access to international financial institutions, such as the International Monetary Fund (IMF), can be crucial to their economic viability (Fazal & Griffiths, 2014). In other words, the perspective of being a “contested state” or one with limited recognition and a high degree of legal and economic insecurity may tilt the balance in favour of the host state. As James Ker‐Lindsay (2012) has persuasively argued, there is evidence that strategies of “counter secession” use fears about the international isolation of a hypothetical new state in their campaigns in favour of the status quo. The prospect of international recognition, however, may embolden secessionist supporters and put an end to existing concerns about the feasibility of the new state. Whereas the first and second hypotheses sought to test the impact of international incentives on the entire population, the third and fourth hypotheses aimed to identify the mechanisms that drive these results. More specifically, the third hypothesis aimed to find out if individuals with fixed political preferences reflected on the international environment or whether they held inelastic political inclinations despite rising costs (e.g., the risk of becoming a pariah state). We follow the literature on secession in assuming that support for independence is largely a function of regional and/or national identity (Sorens, 2005). Although demands for secession do not necessarily stem from the identity‐based distinctiveness of groups, national identity/ies are usually considered the main driving factor of independence support in both the Scottish and Catalan cases (McCrone & Paterson, 2002; Serrano, 2013). We took the self‐reported degree of nationalist sentiment as a proxy for political preferences for (or against) secession, and we follow Anthony D. Smith in defining nationalism as “an ideological movement for attaining and maintaining autonomy, unity and identity on behalf of a population deemed by some of its members to constitute an actual or potential ‘nation’ ” (Smith, 1991, p. 73). The scholarly basis for Hypothesis H3 relied on the literature of partisan identification as a “perceptual screen” (Campbell, Converse, Miller, & Stokes, 1960, p. 133), which shapes the attitudes of individuals towards political objects. According to the research on public opinion, parties structure the political debate and provide citizens with cues that help them to establish their preferences. For example, individuals react differently to similar cases of corruption, depending on whether the responsible politician is a member of their preferred ideological family or of a rival one (Anduiza, Gallego, & Muñoz, 2013). As several studies have shown, the stronger the partisan attachment of individuals, the stronger their tendency to support their own party and dismiss their opponents (Bartels, 2002; Lavine, Johnston, & Steenbergen, 2013; Taber & Lodge, 2006). At the same time, individuals with weaker partisan attachments are more likely to change their preferences in the light of new information (Bartels, 2002). Likewise, previous work on the influence of an EU membership on support for secession has suggested that national identity was a key explanatory variable in explaining independence support and that individuals who identified more strongly with the state or the substate unit were barely influenced by hypothetical international sanctions (Muro & Vlaskamp, 2016). In accordance with previous research on the relationship between national identity and support for independence (Liñeira & Cetrà, 2015), we expect respondents with strong nationalist preferences (either pro‐secession or pro‐host state) to maintain their positions after our primings, even when they were faced with an adverse context of increasing costs. A “hard version of independence” scenario that supported the statist views of Spanish or British nationalists (e.g., no international support for secession) would thus reaffirm their preferences, and this adverse treatment would be ignored as the prospects of international recognition would not alter their preferences towards the status quo. The same could be said about staunch Catalan or Scottish nationalists who would see a possible unilateral declaration of independence as a “once in a lifetime” opportunity for which it was worth paying a hefty cost. For example, during the Scottish campaign, the SNP government produced optimistic economic predictions that ignored Scotland's dependence on oil and gas revenues to support its public services and neglected the negative implications of the volatility of the oil price (Keating, 2017, p. 57). Therefore, our expectation was that the political attitudes of some electors would remain unaltered, even in the face of currency uncertainty and other “unknowns,” such as EU membership or security provisions (e.g., the relocation of the Scottish‐based Trident nuclear programme). Finally, individuals with a moderate degree of nationalist sentiment and dual identities would be more influenced by the adverse scenarios, simply because they had weaker preferences regarding the polarising choice of independence vs status quo. Our third hypothesis was H3.The stronger (weaker) the degree of nationalist sentiment of the individual, the less (more) s/he will be influenced by the information about the prospects of international recognition. Just as the pre‐existing intensity of national sentiment was expected to moderate the effects of the treatment, so did we also wonder whether the motivations for a pro‐secession position would influence the impact of the treatments, which was the justification for Hypothesis H4. The existing literature makes a distinction between ethno‐political, economic, and political–institutional reasons to support independence (Alesina & Spolaore, 1997; Emizet & Hesli, 1995; Gurr & Moore, 1997). Ethno‐politically motivated proponents of secession argue that the host state does not provide adequate channels to express the distinctiveness of their nation (language, culture, ethnicity, religion, etc.) and that only an independent state can guarantee protection (Breuilly, 1994; Guibernau, 2006). Economically motivated secessionists hope that a new state will guarantee that the nation's wealth benefits exclusively its own members and that it will no longer be lost to ethnic or national groups from poorer regions. Existing evidence confirms the idea that, besides having a different identity, relative affluence is also a good predictor for separatism (Sambanis & Milanović, 2011; Sorens, 2005). Finally, support for secession may result from the perception that an individual lives in an unjust political system (Buchanan, 1991). This alleged injustice may be found in an autocratic regime that oppresses its national minorities violently but also in a democratic regime that does not provide sufficient opportunities for the political representation of ethnic groups. In these scenarios, secessionists argue that providing the nation with a political roof is a remedy to defend the national interests in the long term. In most secessionist movements, a combination of these three motivations—ethno‐political, economic, and political–institutional—can be detected, but individuals tend to rank one over the others. Finally, we presumed that pro‐secession nationalists with ethno‐political motivations would be only marginally influenced by the prospects of international recognition, as this new information did not affect how people identified themselves or how they felt about the treatment of their identity. For individuals who were driven by economic or political motivations, however, we expected international recognition to be of greater significance. As previously described, the perspective of being a “contested state,” or one with limited recognition and a high degree of economic and legal insecurity, may shift the economic cost–benefit analysis for individuals who have concerns about the feasibility of the secessionist agenda (Muñoz & Tormos, 2015). Our fourth hypothesis therefore was H4.Substate nationalists who are motivated by ethno‐political arguments will be less influenced by the information about the prospects of international recognition than substate nationalists who are motivated by economic or political–institutional arguments. To recapitulate, our hypotheses aimed to confirm the following mechanism: The prospects of international recognition typically influence individuals with moderate nationalist preferences as well as secessionist‐leaning participants who emphasise political and/or economic motivations. By contrast, the preferences of staunch pro‐secession nationalists, especially those who highlight ethno‐political motivations, remain unaltered by the additional information provided in the vignettes. Similarly, pro‐host state nationalists are only marginally influenced by diplomatic recognition, as they prefer the status quo in any case above secession. The mechanism is further clarified in the following section, where we explain how we embedded an experimental design in an opinion survey in order to measure the impact of the international environment on domestic preferences for secession.

3 SURVEY EXPERIMENT A survey experiment is a deliberate manipulation of a survey instrument “for purposes of inferring how public opinion works in the real world” (Gaines, Kuklinski, & Quirk, 2007, pp. 3–4). The word “experiment” also implies a random assignment of respondents to control and treatment conditions. Comparing the judgments and opinions of the respondents in the treatment groups to those in the control group reveals the causal effects under investigation. Survey experiments are increasingly used because they are relatively affordable to implement and because they provide grounded inferences about how citizens make decisions and respond to real‐world political objects. In our case, we wanted to confront respondents with credible scenarios and could not rely on conventional survey data to enhance our understanding of the international dimension of secessionist politics. We designed and administered a large‐scale Web survey in May 2014, when both Catalonia and Scotland were engaged in intense public debates about their possible independence.1 These two cases are often compared in the literature on territorial politics because of their numerous similarities (Cetrà & Harvey, 2018; Guibernau, 2006; Keating, 2001). In our case, we adopted a Most Similar Systems Design, which reduced the number of possible explanations for the outcome variable and allowed us to focus on the variation across the cases. Approximately 2,400 respondents were presented with a list of 38 questions, which they could answer in their preferred language (in Catalonia and in either Catalan or Spanish). The sample in both regions was of 1,200 respondents, which we divided into three representative subgroups of 400 individuals. Each group was representative in terms of age, gender, and place of residence (in Scotland: council areas; in Catalonia: provinces). A survey firm with ample experience in commissioning national and international representative surveys administered our survey experiment, which was designed to measure how priming affected an opinion or attitude towards state birth. Spain does not permit the secession of Catalonia, but there is broad international support for a unilateral declaration of independence. Several great powers have already declared that they would recognise the new state. The survey experiment randomly assigned respondents alternative versions of questionnaire items. In our case, we assigned three different treatments (positive, negative, and neutral) to six representative samples in Catalonia and Scotland. Our respondents in Catalonia with a positive treatment received the scenario below, before they were asked whether they were in favour of a unilateral declaration of independence by the Catalan Parliament or not, under the described circumstances. We deliberately used the vague term “great powers,” so that respondents could interpret it the way they wanted. For European respondents, for example, Germany's stance on this issue is probably more relevant than India's or China's. These “great powers” carry the most weight in the EU, and their positions would also influence the prospects of EU membership for the new state. Spain does not permit the secession of Catalonia, and there is no international support for a unilateral declaration of independence. Not a single country has declared that it would recognise the new state, and some great powers have already rejected this outright. The same applied to the respondents with a negative treatment, who received this vignette: There is also talk about the possibility of a unilateral declaration of independence of Catalonia by the Catalan parliament. We want to ask you a number of questions about this topic. A third control group was used as a reference group and only received the following information: This control group made it possible to measure the variation between the control subgroup and the positive and negative subgroups, as well as to test the impact of the vignettes. Before we go any further, it is important to briefly talk about the context in which the survey experiment was conducted. Due to space constraints, this description can only be a cursory examination of the different political, social, and legal situations in the two places (see Muro, 2018; Keating, 2017, for more detailed overviews). In the case of Catalonia, the movement of vindication that advocated for the political–cultural recognition of Catalonia within Spain (e.g., Catalanism) was dominant since the transition to democracy in the late 1970s. Secessionism was traditionally weak but gained considerable strength in the late 2000s. Although its strengthening coincided with the Great Recession, Cuadras‐Morató and Rodon (2017) show that economic grievances resulting from the crisis did not play a significant role in changing attitudes towards secessionism. Instead, the reasons for its growth are related to the failed process of autonomy reform in 2010 (Orriols & Rodon, 2016; Rico & Liñeira, 2014), which was framed by nationalist parties as the end of meaningful self‐government (Basta, 2018). As Muro explains, the independence campaign “was originally a bottom‐up social movement of extraordinary energy” but “elites soon maneuvered to take control” (Muro, 2018, p. 86). At the point when we carried out our survey experiment, the regional government had already laid out a road map towards political independence. The first step was a consultative referendum on independence, which was scheduled for 9 November 2014. In case the Spanish state prevented this referendum from happening, the regional government wanted to hold “plebiscite” elections to count how many Catalans would vote for independence. If these elections showed that the majority of Catalan voters favoured secession, then the required steps towards political independence would be taken, including the possibility of a unilateral declaration of independence by the Catalan regional parliament (all three steps eventually took place). As the Spanish Constitution does not permit the secession of a part of the country's territory, the Catalan government knew that the two available options were a (very unlikely) constitutional reform or unilateral steps. The road ahead was likely to be bumpy, and even the Catalan government's expert group concluded that “the recognition and integration in international society of a new state is a complex and gradual process which can take years, and depends on many political factors as well as legal ones” (Advisory Council on the National Transition, 2014, p. 8). Due to this situation, the Catalan executive put great effort in “internationalizing the conflict” and attracting support in the rest of world (e.g., by establishing government delegations in 11 countries and training officials for diplomatic service; Muro, 2018, p. 86). In order to frame their efforts in a broader international context, they referred frequently to the referendum in Scotland as an example Spain should follow (the Spanish government's response was that the legal and constitutional situations in Spain and the UK were too different to make these cases comparable). The perception of our respondents in Catalonia, at that point, was thus that a unilateral declaration of independence was a possibility but not something that was expected to happen within a short time period. 2012 In the referendum, Scotland votes in favour of independence and the UK is reluctant to accept this outcome. There is widespread international support for a unilateral declaration of independence. Several great powers have already declared that they would recognise the new state. By contrast, the UK government took a different approach to the issue of Scottish independence and allowed a referendum that could “deliver a fair test and decisive expression of the views of people in Scotland and a result that everyone [would] respect” (UK Government and Scottish Government,, p. 3). In October 2012, Scottish First Minister Alex Salmond and UK Prime Minister David Cameron signed the Edinburgh Agreement, allowing Scotland to hold an independence referendum. Due to this different political and legal context, the Scottish government did not have the same need for gathering international support as their Catalan counterparts had: Unilateral steps were not required if the referendum was won. Given the inherent uncertainty of Scottish independence as a proposition, Scottish public opinion concentrated on the middle ground, with the largest segment of the population still favouring a third way between union and independence. Due to the consensual agreement and the acceptance of the bid for independence by the home state, we had to formulate our treatments somewhat differently to make remedial action more plausible to Scottish respondents. As a result, the modified positive treatment ( H1 ) was ‘In the referendum, Scotland votes in favour of independence and the UK is reluctant to accept this outcome. There is no international support for a unilateral declaration of independence. No country has declared that it would recognise the new state, and some have flatly ruled it out.’ The respondents with the negative vignette ( H2 ) received the following: In the referendum, Scotland votes in favour of independence and the UK is reluctant to accept this outcome. Finally, the respondents with a “neutral” treatment received this vignette: Table 1 (above) shows the support for a unilateral declaration of independence by treatment in Catalonia and Scotland. In order to measure the effect of the treatments, we ran several logistic and treatment effect models that included a series of control variables (see Table A3a and A3b). These control variables included the respondent's gender, age, education level, place of residence, language spoken at home (in Catalonia), political orientation on a left–right scale, work situation, income level, and whether they had lived outside the country for a period longer than 6 months. We added this final variable because we assumed that respondents who had been exposed to life abroad might be more susceptible to changes in the international scenario. Table 1. Support for a unilateral declaration of independence by treatment in Catalonia and Scotland Pro‐independence Catalonia Scotland NO YES Total NO YES Total Treatment Negative 200 (36.23) 198 (30.41) 398 (33.08) 230 (36.45) 171 (29.79) 401 (33.28) Control 196 (35.51) 208 (31.95) 404 (33.58) 210 (33.28) 192 (33.45) 402 (33.36) Positive 156 (28.26) 245 (37.63) 401 (33.33) 191 (30.27) 211 (36.76) 402 (33.36) Total 552 (100) 651 (100) 1203 (100) 631 (100) 574 (100) 1205 (100) For Hypothesis H3, we asked the participants how they identified themselves in terms of national belonging to measure their degree of nationalism (Centre d'Estudis d'Opinió, 2015; Scottish Referendum Study, 2014). We asked the participants the so‐called “Linz‐Moreno question” (Moreno, 2006), which allows individuals to classify themselves (e.g., in the case of Catalonia) as feeling “Only Catalan,” “More Catalan than Spanish,” “Both Catalan and Spanish,” “More Spanish than Catalan,” or “Only Spanish.” The two extremes we defined as representing the highest degree of nationalist sentiment. These self‐definitions did not overlap with ethnic backgrounds per se, as in public both Catalan and Scottish nationalist leaders promote a “civic nationalism” that is also open to individuals whose background is outside the region (Mycock, 2012; Serrano, 2013). As has been done in comparable studies (Muñoz & Tormos, 2015; Rico & Jennings, 2012), we decided to lump together the answers of the two groups of respondents: those who felt more “British than Scottish” with “Only British” and those who felt more “Spanish than Catalan” with “Only Spanish.” This choice was motivated by a practical and a theoretical reason. The practical reason was that very few respondents identified themselves exclusively or predominantly with “Spain” or “Britain.” By combining these two categories, it was possible to obtain a larger sample.2 Theoretically, these two groups were merged because we did not expect any significant difference in their responses. Guinjoan and Rodon's (2016) detailed methodological study on the Linz‐Moreno question suggests that, for Catalan identities, the categorical question performs well in capturing the intensity of nationalism. This is not the case for Spanish identities, where the mixed categories also capture a large degree of Spanish nationalism. This is because, “as previous research has argued, this may have to do with the strong connections that most Catalan citizens make between Spanish identity and right‐wing values, which are still seen as rooted in the Francoist dictatorship tradition (Dinas, 2012)” (Guinjoan & Rodon, 2016, p. 139). In Catalonia—and we assume the same pattern holds for Scotland—both auto‐identifications can therefore be interpreted as a sign of a comparably strong bond with the host state. In order to test Hypothesis H4, we asked our respondents two questions. First, we simply asked the respondents what they would vote in a referendum on independence. If they opted in favour of secession, we provided them with a list of possible reasons for their choice, among which figured ethno‐political, economic, and political–institutional options. The respondents could choose up to three motivations to explain their choice. Using these answers, we could then construct a dummy variable “use of ethno‐political argument” to distinguish between those respondents that had used at least one of these arguments and those who had not (the list of motivations can be found in Appendix A).

4 RESULTS AND DISCUSSION The goal of the Web‐based survey experiment was to test the extent to which support for a unilateral declaration of independence could be mediated by international incentives of recognition (both positive and negative). To measure the impact of international threats and payoffs on the respondents' support for secession we estimated the average treatment effect (ATE), a parameter that measures the difference in mean outcomes for treated and untreated units. The expression “treatment effect” is basically the difference between an outcome variable of interest (in our case, support for a unilateral declaration of independence) for individuals who were exposed to the treatment and individuals who were in the control groups. Our first hypothesis (H1: International recognition will have a positive effect on support for a unilateral declaration of independence) could be confirmed in both Catalonia and Scotland. As can be seen in Figure 1, controlling for all the other variables included in the model, the prospect of international recognition after secession had a positive and significant treatment effect on support for remedial action, which is often taken in response to a situation of oppression, exploitation, or domination. In both Catalonia and Scotland, the probability grew by nine percentage points compared to the neutral treatment, and a majority of the respondents supported a unilateral declaration of independence under these conditions. The similarity of results in both cases is striking, particularly when considering the differences between the legal and political contexts in which the hypothetical unilateral declarations of independence of Catalonia and Scotland were set. Ultimately, the findings confirm the expectation that domestic support for a unilateral declaration of independence will increase when the international context is favourable to state birth. Figure 1 Open in figure viewer PowerPoint Average treatment effects on support for unilateral of independence in Catalonia and Scotland with 95% CIS Our second hypothesis (H2: The lack of international recognition will have a negative effect on support for a unilateral declaration of independence) could not be confirmed by the randomised trial, as indicated in Figure 1. There was no significant decrease in support for a unilateral declaration of independence after the negative treatment by comparison with the control group. The reason for the lack of effect could be that respondents were affected by real‐life events or information. For example, the experiment could not isolate respondents from previous negative priming during the independence campaign. In the case of Scotland, various actors highlighted the political and economic uncertainties that an independent Scotland would face. Former Prime Minister Gordon Brown, one of the key spokespersons for the “No” side, argued that “Scottish sovereignty” was a “19th‐century answer to 21st‐century challenges,” whereas former US President Bill Clinton said he worried that a “long, complex negotiating process” with the UK would weaken the Scottish economy. None of the supporters of the Better Together campaign warned of international ostracism, but they did highlight the economic risks and uncertainties of independence (Beasley & Kaarbo, 2018). In addition, the survey experiment could not measure if previous events, such as Kosovo's unilateral declaration of independence in 2008 (whose status is still contested), had already shaped the attitudes of respondents. According to Bruno Coppieters, “the recognition of Kosovo by Western governments had a major impact on all secessionist conflicts in which external actors have a strong presence” (Coppieters, 2010, p. 252). Especially in the Catalan case, due to its different characteristics, the Kosovo example was mentioned repeatedly in televised head‐to‐head debates and the press. For example, the Spanish Deputy Prime Minister Sáenz de Santamaria asked publicly whether Catalans wanted to “identify themselves with Kosovo, where the level of unemployment is at 40 percent and which has a per capita income 25 times smaller than that of Catalonia” (La Vanguardia, 15 March 2013). In other words, the participants of our survey experiment could have concluded that the negative treatment was the status quo and did not perceive the new information as a “game changer” with Kosovo's situation in mind. In any case, the puzzling absence of any effect of the negative treatment resonates with previous work on the prospects of EU membership for secessionist movements, which also observed a similar result and explained it by referring to the real‐life warnings about possible EU exclusion around the time the survey was carried out (Closa, 2016; Keating, 2017). Our third hypothesis (H3: The stronger (weaker) the level of nationalism in the individual, the less (more) s/he will be influenced by the information about the prospects of international recognition) sought to test the extent to which the intensity of nationalism could mediate the impact of our treatments. We looked at the average marginal effects—calculated by varying the focal variable (in this case the level of nationalism)—while keeping all covariates of our model as they were observed. As it can be observed in Figure 2, respondents behaved in accordance with our hypothesised expectations that more nationalist individuals were less likely to be influenced by the treatments. In both cases, the group “feeling more Catalan than Spanish/feeling more Scottish than British” was the most affected subgroup, and support for a unilateral declaration of independence became substantially more likely after the positive treatment by comparison with the control group (19 percentage points more in Catalonia and 23 percentage points more in Scotland). Furthermore, in both categories, the results after a positive treatment for “feeling both Catalan and Spanish/feeling both Scottish and British” were also significant (15 percentage points more in Catalonia and 17 percentage points more in Scotland). The more nationalist subgroups—both in favour of the seceding region and the host state—were not affected by the treatments. There was, admittedly, a ceiling effect for these subgroups, as our treatments had no effect on their responses: Support for a unilateral declaration of independence was above 90% for pro‐secession nationalists and below 10% for state nationalists in the control group. It is, however, still noteworthy that pro‐secession nationalists were not influenced by the negative treatments, in the same way that pro‐state nationalists were not influenced by the positive treatments. The negative treatment had no significant influence on any of the subgroups. These results support earlier findings by Muñoz and Tormos about the economic drivers of secessionism in Catalonia: Individuals with strong identity and partisan beliefs were much less influenced by economic arguments than more “moderate” individuals (Muñoz & Tormos, 2015). Figure 2 Open in figure viewer PowerPoint Average marginal treatment effects on support for unilateral of independence in Catalonia and Scotland by national identity with 95% CIS Hypothesis 4 (H4: Substate nationalists who are motivated by ethno‐political arguments will be less influenced by the information about the prospects of international recognition than substate nationalists, who are motivated by economic or political–institutional arguments) could also be confirmed. As illustrated in Figure 3, participants who had not used any ethno‐political argument were the only subgroup that was to a statistically significant degree influenced by the positive treatments in both places. In Catalonia, the probability of supporting a unilateral declaration of independence grew with 8.1 percentage points, compared to the control group. In Scotland, support for a unilateral declaration of independence went up by nine percentage points among respondents that had not used any ethno‐political arguments. In short, these findings suggest a typological distinction between those who support secession for ethno‐political motivations, on the one hand, and those who support secession for “economic” or “political–institutional” reasons, on the other. Further operationalisation of these normative types of voters could improve empirical predictions on future votes on independence as well as contribute to the ethnic‐civic dichotomy in nationalism studies (Brubaker, 2004). Figure 3 Open in figure viewer PowerPoint Average marginal treatment effects on support for unilateral of independence in Catalonia and Scotland by motivations with 95% CIS

5 CONCLUSION Secessionist goals are set at the domestic level, but they require international recognition to be fully realised. Our findings suggest that having the support of foreign powers increases popular support for a unilateral declaration of independence among stateless nations with vigorous secessionist movements. International recognition hardens public support for a unilateral declaration of independence, but our results also indicate that the impact of international factors is not homogeneously distributed among the populations of our relatively affluent case studies. The research findings can be summarised in the following three points: First, the issue of international recognition influenced the opinions of respondents in both Catalonia and Scotland. In our survey experiment the positive treatment—broad international support for independence—increased support for a unilateral declaration of independence at a statistically significant level. This result was consistent with existing scholarship on the role of international recognition offering states “an additional instrument with which to promote public support for controversial and contested solutions to self‐determination conflicts” (Shelef & Zeira, 2015, p. 19). The negative treatment—no international recognition—did not have a significant impact, most probably due to a contamination effect. The survey experiment could not replicate lab conditions, which meant that respondents in our sample had already been exposed to negative priming in real life. Unionist pundits had previously warned voters about the detrimental implications of taking unilateral steps that could result in a break‐up. That prior exposure could explain why there were minor differences between respondents exposed to our “neutral” and “negative” treatments and hence the small variation measured. Second, the treatment effects were strongly mediated by the respondents' prior degree of nationalist sentiment. The expectation was that individuals with exclusive identities would not change their political attitudes towards secession simply because they were exposed to a brief priming in an online questionnaire. Indeed, the more nationalist a respondent was, the less likely s/he was to be affected by any of our vignettes regarding a possible unilateral declaration of independence. However, the truly interesting finding was to identify which individuals were more likely to change their cost–benefit analysis according to treatments. Middle‐ground voters with moderate nationalist beliefs (and shared identities) were significantly more influenced by our fictitious scenarios about international recognition affecting their preferences for setting up of a new independent state without the consent of the host state. This is an important finding, because a majority of electors in both Scotland and Catalonia are risk averse, have multiple identities, and favour a third way between union and independence (Keating & McEwen, 2017; Liñeira & Cetrà, 2015). Third, the results demonstrated that the pro‐secessionist participants driven by economic or political–institutional motivations were more likely to be influenced by international incentives (both positive and negative) than those participants who had provided ethno‐political explanations for their choice. The distinction between drivers of secession is well established in the literature on nationalism (Alesina & Spolaore, 1997; Emizet & Hesli, 1995; Gurr & Moore, 1997), and the underlying logic in our study was to discriminate between individuals who were making ethno‐political arguments about a distinct identity and those who wanted their nation to have more political power and/or financial resources. Whereas economic and political disputes can sometimes be settled with increasing devolution and additional funding, it is difficult to reach a middle point or compromise when the ultimate goal is to have a perfect correspondence between political and cultural boundaries (Gellner, 1983, p. 1). Ethno‐politically driven nationalists were less susceptible to the treatments, because their identity concerns were neither positively nor negatively affected by the international scenarios provided. Further research is needed to identify how real‐world actors use and merge these normative arguments in favour of self‐determination (Dalle Mulle & Serrano, 2018). While the two case studies under examination allow us to explore the importance of international recognition in non‐violent territorial disputes, they also raise potential concerns regarding the generalisability of our findings. First, it is difficult to argue that the findings may be relevant to the whole universe of cases where two entities disagree over the possession or control of land. The two relatively affluent case studies are located in Europe, where secessionist movements are more concerned about the issue of EU membership than that of international recognition per se. Also, the EU is a union of states that has repeatedly stated its support for territorial integrity, democratic means, and preferences for gradual change, as long as they are agreed by the secessionist region and the host state (Closa, 2016). Second, the findings might not be directly applicable to violent and post‐conflict contexts, where the citizens are more concerned about the short‐term survival of their state through military and economic support than long‐term recognition. In these cases, the material and symbolic support of one powerful patron carries more weight in the domestic calculations than the more abstract recognition of the international community (see, e.g., Transnistria and the Republic of Artsakh [Nagorno Karabakh]). Third, and in a more practical sense, it may also be difficult for citizens of secessionist regions in oppressive regimes to gather reliable information about the level of international support for their cause. In these cases, sound information on the positions of international players may not be easily accessible to domestic audiences. In terms of policy implications, domestic considerations are central in accounting for independence support. At the same time, the issue of international recognition can influence domestic support for a unilateral declaration of independence, which means that international powers can never be fully neutral. Having the support of great powers, the United Nations, or the EU, can create an environment in which radical steps are legitimated and “political divorces” are seen as legitimate answers to territorial disputes. By contrast, a global scenario that is hostile to maximalist demands for self‐determination and favours minority rights, shared sovereignty, and federal solutions as instruments of conflict resolution might reduce the domestic support for a unilateral declaration of independence and incentivise secessionists to moderate their political strategy. As Fazal and Griffiths remark, “these groups are so eager for recognition, they may be especially likely to respond to the suggestions of the international community” (Fazal & Griffiths, 2014, p. 110). Regardless of the situation, international players are constantly taking sides, either when they remain silent and support the status quo or when they express their preferences for state dissolution. International players who refuse to position themselves on a territorial conflict by arguing that they do not want to interfere in a domestic dispute are not washing their hands; they are silently supporting the player with more leverage, namely, states.

FUNDING This work was supported by the Fritz Thyssen Foundation under Grant number Az.20.14.0.032.

ENDNOTES 1 We acknowledge that the idea of a unilateral declaration of independence was a less credible scenario in Scotland than in Catalonia. However, as the remainder of this paper shows, the results were very similar in both cases hence confirming the validity of our priming.

We acknowledge that the idea of a unilateral declaration of independence was a less credible scenario in Scotland than in Catalonia. However, as the remainder of this paper shows, the results were very similar in both cases hence confirming the validity of our priming. 2 Feeling “More Spanish than Catalan” had 82 observations, and feeling “Only Spanish” had 47 observations. By combining these two categories, we had 129 observations, which represented 11.28% of our respondents. In Scotland, “More British than Scottish” had 96 observations and “Only British” 102 observations. Together, they represented 17.7% of the respondents.

Appendix A.: TECHNICAL DETAILS OF THE SURVEY Geographical scope of the survey: Autonomous Community of Catalonia (Spain) and Scotland (United Kingdom). Universe: individuals residing in the area of study older than 18. Size and distribution of sample: 1,203 interviews in Catalonia and 1,205 interviews in Scotland. The respondents were divided into representative subgroups of 400 individuals, applying the age, gender, and place of residence quotas (in Catalonia: provinces; in Scotland: council areas). Sampling error: for a confidence level of 95.5% (as is usually adopted) and assuming the principles of simple random sampling, in the worst‐case scenario of maximum uncertainty (p = q = 50%), the sampling error corresponding to the data on the total sample is 3.2 percentage points. Method of collecting information: online survey, using structured and pre‐coded questions. The task was carried out by Netquest, using their databank of respondents. The questionnaire was available in Spanish and Catalan (Catalonia) or English (Scotland). Table A1. Motivations to support Yes‐vote in independence referendum Ethno‐political motivations Economic and political–institutional Catalonia (Scotland) is a separate nation of Spain (the UK). The economic situation in Catalonia (Scotland) would improve with an independent state. Only an independent state can guarantee the identity and language of Catalonia (Scotland; in the Scottish survey without “and language”). Catalonia (Scotland) would manage its financial resources better (e.g., taxes). I feel Catalan (Scottish). Catalonia (Scotland) would have more power to govern its own affairs. Other (recoded if the motive given by the respondent fit in this category) Catalonia (Scotland) could defend its interests better in the world. To promote more powers for Catalonia (Scotland) within Spain (the UK; a “tactical vote”) Other (recoded if the motive given by the respondent fit in this category) Table A2. Descriptive statistics CAT SCOT Variable Observations M (std. dev.) Observations M (std. dev.) Min Max National Id. 1,143 2.25 (0.99) 1,116 2.34 (1.05) 1 4 Female 1,203 1.51 (0.50) 1,205 1.55 (0.50) 1 2 Age (categories) 1,203 4.59 (1.50) 1,205 4.04 (0.96) 1 6 Education 1,159 2.66 (0.80) 1,122 2.50 (0.97) 1 4 Language 1,181 1.87 (0.88) 1 3 Political discussion 1,203 2.42 (0.90) 1,205 2.67 (0.97) 1 4 Ideology 1,203 3.69 (1.79) 1,205 4.67 (1.77) 0 10 Occupation 1,158 2.31 (1.56) 1,125 1.75 (1.45) 1 6 Personal income 1,012 3.11 (2.35) 1,104 2.57 (1.89) 1 8 Lived outside 1,203 1.80 (0.40) 1,205 1.84 (0.37) 1 2 Motivations 1,000 0.91 (0.29) 1,109 0.94 (0.24) 1 2 Table A3. Average marginal effects for models in Catalonia and Scotland Table A3a: Catalonia Variables Model 1 Model 2 Model 3 Model 4 Model 5 Treatment (ref. Control) Negative −0.017 (0.035) 0.001 (0.032) −0.003 (0.035) −0.002 (0.032) −0.000 (0.035) Positive 0.096*** (0.035) 0.090*** (0.031) 0.078** (0.035) 0.089*** (0.031) 0.080** (0.035) Nationalisma National Id. (ref. Both) 0.072** (0.031) 0.074** (0.032) Only Catalan 0.576*** (0.056) 0.575*** (0.056) More Catalan 0.414*** (0.055) 0.413*** (0.054) Spanish −0.177*** (0.059) −0.176*** (0.059) Education Language (ref. Both) −0.035** (0.018) −0.030 (0.019) −0.034* (0.018) −0.031 (0.019) Catalan 0.035 (0.038) 0.184*** (0.043) 0.034 (0.038) 0.182*** (0.043) Spanish −0.122*** (0.047) −0.381*** (0.048) −0.122*** (0.047) −0.376*** (0.048) Political Discussionb −0.009 (0.016) −0.024 (0.017) −0.009 (0.016) 0.044 (0.031) Ideology −0.018** (0.008) −0.046*** (0.008) −0.018** (0.008) −0.045*** (0.008) Lived Outside 0.064* (0.033) 0.032 (0.037) 0.063* (0.033) 0.030 (0.037) Non‐Ethnic Reasons 0.044 (0.050) 0.071 (0.054) 0.059 (0.052) 0.075 (0.054) No‐Nationalist X Positivec 0.129*** (0.046) Non‐Ethnic X Positive 0.087*** (0.033) No‐Discussion X No‐Nationalist X Positive 0.180*** (0.064) Observations 1,203 757 757 757 757 Controlsd No Yes Yes Yes Yes Table A3b: Scotland (1) (2) (3) (4) (5) Variables Model 1 Model 2 Model 3 Model 4 Model 5 Treatment (ref. Control) Negative −0.035 (0.036) −0.031 (0.036) −0.028 (0.040) −0.032 (0.036) −0.037 (0.040) Positive 0.060* (0.036) 0.089** (0.036) 0.079** (0.040) 0.089** (0.036) 0.079** (0.040) Nationalisma National Id. (ref. Both) 0.050 (0.033) 0.055 (0.033) Only Scottish 0.470*** (0.042) 0.470*** (0.042) More Scottish 0.325*** (0.040) 0.326*** (0.040) British −0.047 (0.044) −0.048 (0.044) Education 0.025 (0.017) −0.011 (0.018) 0.024 (0.017) −0.007 (0.018) Political Discussionb −0.050*** (0.015) −0.066*** (0.017) −0.050*** (0.015) 0.098*** (0.035) Ideology −0.043*** (0.008) −0.057*** (0.009) −0.043*** (0.008) −0.057*** (0.009) Lived Outside 0.068 (0.044) 0.029 (0.048) 0.069 (0.044) 0.025 (0.048) Non‐Ethnic Reasons −0.070 (0.065) −0.089 (0.077) −0.080 (0.062) −0.083 (0.078) No‐Nationalist X Positivec 0.110** (0.052) Non‐Ethnic X Positive 0.101*** (0.037) Discussion X No‐Nationalist X Positived 0.165** (0.069) Observations 1,205 846 846 846 846 Controlse No Yes Yes Yes Yes