Immigrants’ acquisition of national citizenship in Portugal and Spain: the role of multiculturalism?

Against the backdrop of a restrictive backlash in Europe, this article examines Portugal and Spain’s policies on immigrants’ acquisition of their national citizenships and assesses their potential convergence towards a common model. Drawing on a qualitative comparative analysis, this investigation also seeks to understand the evolution of the two Iberian countries’ approaches by exploring the dominant theories on the variation of citizenship regimes. A significant degree of policy convergence over an assimilationist model was identified between the early 1990s and the mid-2000s. Thereafter, Portugal shifted towards a multicultural model, whilst policy stability was observed in Spain. Policy variation between the two countries was mostly associated with the role of political ideas, in particular the centre-left parties’ commitment to multiculturalism. Furthermore, this investigation highlights the divergence of Portugal’s approach from the wider restrictive backlash supposedly observed in Europe, whilst Spain continues to uphold an assimilation model in the twentieth-first century. ARTICLE HISTORY Received 3 June 2019 Accepted 23 November 2019

Contrary to the expectations of post-national theories that citizenship would lose relevance because civic and social rights would be ascribed to the universal 'personhood' rather than by national belonging (Soysal 1994), citizenship became an increasingly contested issue in the political systems of Western European states in the 21st century (Goodman and Howard 2013). This trend was evidenced by French President François Hollande's controversial proposal to strip dual citizenship from convicted terrorists in the aftermath of the 2015 Paris terrorist attacks (Carvalho 2019). Thus, the transnational forces of post national membership involving the intense interdependence promoted by globalisation and the emergence of the human rights regime (Soysal, 1994, p.144) failed to prevent the politicisation of this topic or to curtail the national governments' prerogative to unilaterally set the criteria regulating immigrants' access to full membership of their political communities (Shachar et al. 2017). Similarly, the integration process within the European Union (EU) and the creation of European citizenship lacked any influence over the regulation of political membership by member-states (Koopmans, Michalowski, and Waibel 2012). Consequently, citizenship policies continue to be regarded as important indicators of a host society's acceptance or rejection of its foreign citizens (Janoski 2010).
Two distinct waves were identified in the comparative literature on immigrants' access to national citizenships (Baubock et al. 2005). Throughout the 1990s, a cross-national convergence was observed throughout Western Europe, as naturalization became regarded as an instrument employed by host states to promote foreign citizens' integration (Hansen and Weil 2001). This liberal perception fostered the promotion of more inclusive pathways for second-generation immigrants, reduction of residence criteria for gaining access to naturalization, and an increasing tolerance towards dual nationality. From the 2000s onwards, a restrictive backlash was observed in Europe involving the mounting politicisation of this topic and the introduction of new restrictions on immigrants' acquisition of national citizenships (Odmalm 2007;Joppke 2010). This shift included the introduction of civic requirements, involving tests to assess the candidates' language proficiency and their knowledge of national culture, as well as limitations on dual nationality. Yet, the accuracy of references to a broader restrictive shift have been disputed in the literature (Goodman and Howard 2013).
Within this context, this article compares Portugal and Spain's policies concerning immigrants' acquisition of their national citizenships in order to assess their potential convergence towards a similar, Iberian model. The theories of liberal convergence follow to two distinct perspectives: first, this political process was associated with the diffusion of supranational norms, the emergence of a global human rights regime and the adherence to liberal principles emphasised by post-national theories (Sassen 1996). Secondly, other proposals highlight the influence of endogenous political factors, such as path dependence or judicial intervention, as the causes behind the convergence towards more inclusive citizenship laws aimed at foreign citizens (Freeman 2006). In sum, both perspectives suggest that citizenship rights became more inclusive, as cultural assimilation requirements were increasingly abandoned by host states, whilst national differences regarding immigrants' acquisition of national citizenship have diminished (see Koopmans, Michalowski, and Waibel 2012) Moreover, Portugal and Spain are recurrently categorized under a single 'exceptional model of immigration' alongside Italy and Greece due to similar structural factors (see Peixoto et al. 2012). However, comparative research on immigrants' rights suggests that variation regarding immigrants' rights at the European level intensified between 1980(Koopmans, Michalowski, and Waibel 2012, whilst intense differences between European nations were highlighted by cross-national research on naturalization policies (Howard 2009). Likewise, this research will emphasize a salient divergence between the two Iberian nations. Whereas Portugal dropped the assimilationist approach in favour of a multicultural model in the mid-2000s, a similar shift is yet to be observed in Spain in the late 2010s. Furthermore, the Portuguese 2018 nationality law deviates from the wider restrictive backlash observed in Europe unlike the policy developments observed in Spain in the early 2010s.
Secondly, this investigation seeks to understand the evolution of the Portuguese and Spanish approaches regarding immigrants' acquisition of their national citizenships by comparing different hypotheses derived from comparative politics (Vink 2018). After the in-depth analysis of the selected case studies, the identified causal relationships will be evaluated through a comparative synthesis. This qualitative comparative analysis involves the employment of a most similar case studies research design due to the relevant features the two countries have in common (Landman 2008). This small-N research strategy is regarded as more valuable for assessing the arguments concerned with causal necessity and/or sufficiency in specific cases than for providing quantitative estimates of the magnitude of a causal relationship (George and Bennett 2005). The comparative analysis indicates the limits of the available theories in understanding the lack of policy liberalization in Spain and the overall lack of convergence between the Iberian states' approaches to immigrants' acquisition of national citizenship.
The divergence between the two countries is associated with the role of political ideas among the political elite (Bleich 2003;Boswell and Hampshire 2017;Pasetti 2019). This investigation suggests that policy liberalization in Portugal was associated, foremost, with the centre-left party's full commitment to multiculturalism in conjunction with a centreleft government incumbency and the absence of anti-immigration parties. Whereas the last two causal factors were observed in Spain during the selected timeframe, their presence failed to prompt policy liberalisation. In short, this research highlights the divergences between the Iberian nations due to Spain's maintenance of cultural assimilation criteria in the twentieth-first century and seeks to understand the evolution of their national approaches through a comparative analysis. The next two sections develop the theoretical background that support this investigation.

Models of incorporation of immigrants
In the early 2000s, Castles and Miller (2003) proposed a tripartite typology to classify the incorporation of immigrants in the most industrialized nations. In the differentially exclusionary model, state membership is conceived as 'a community of birth and descent', and the access to citizenship is characterized by the dominance of 'jus sanguinis' (right of blood) instead of 'jus soli' (right of soil) as well as by restrictive naturalization rules. Immigrants' integration is restricted to specific sectors of the society (labour market) and simultaneously excluded from other areas of the public sphere (such as access to civil, political and social rights), which enhances the perception of being 'second-class' citizens. In the assimilationist model, the state welcomes immigrant integration in the host society but only of those candidates who demonstrate assimilation of the linguistic, religious and cultural traits of the nation. Thereby, immigrants ought to abandon their native customs and to necessarily incorporate the dominant cultural practices of the host society following the state's preference for social homogenization.
Access to nationality is granted to the first generation of immigrants after proof of assimilation, whilst the second generation's access depends on modified 'jus soli' (where the immigrant descendants born in the host state are granted citizenship at majority) or double 'jus soli' (where immigrant dependents born in the country are automatically granted national citizenship at birth). Here, the assumption is that those born and raised in the host society will more easily assimilate than their parents. In the multicultural model, host states grant equal rights to immigrants in all spheres of society (except for political rights), because their full integration in civil society is desirable and actively promoted by the authorities. The process of naturalization for first-generation immigrants is very accessible, whilst unconditional 'jus soli' for second-generation immigrants is perceived as the norm in the multicultural model. Ethnic diversity is tolerated or promoted whilst double nationality is accepted on a universal basis.
Notwithstanding the ambiguity engulfing its definition (Koopmans 2013), multiculturalism will be discussed only in regard to immigrants' acquisition of national citizenships. Thereby, the liberal variant focusing on government policies to ensure the positive recognition of diversity and minorities' cultural and religious rights or the assessment of the backlash against this ideology is excluded from this analysis (Wright and Bloemraad 2012). The proposed typology has been criticized for their static, mutually exclusive character of the three models and the lack of a theory of change. To overcome this problem, a set of hypotheses derived from the literature on the variations of citizenship regimes will be compared in order to understand the liberalisation of immigrants' access to national citizenships (Vink 2018). 1 Drawing on path dependence, it was argued that former colonial powers that experienced early democratization processes adopted more liberal citizenship regimes (Howard 2009). Others suggested that the effects of colonialism vary according to the degree and duration of the colonisation period (Hansen 2002;Janoski 2010). Thus, the first hypothesis proposes: H1the liberalization of the foreign citizens' access to Portuguese and Spanish national citizenships is incentivized by these countries' special ties to their former colonies.
A second hypothesis looks at the liberal direction of policy reforms by exploring the political ideology of the national governments (Howard 2009;Koopmans 2013). Whereas left-wing governments are associated with de-ethnicization (which lowers the threshold for immigrants' acquisition of citizenship) following their demands for universalism and equality, right-wing governments are linked to re-ethnicization (reinforcing the ties with foreign-born generations; Joppke 2010). So, the second hypothesis explores the extent to which: H2the liberalization of the foreign citizens' access to Portuguese and Spanish national citizenships is enhanced by left-wing parties' government incumbency.
The third hypothesis highlights the absence of anti-immigration parties in the national party systems as the most important factor behind the liberalization of immigrants' acquisition of national citizenships (Howard 2009;Hansen and Clemens 2018). The xenophobic mobilization of the electorate by extreme-right parties promotes public hostility towards immigration and trumps the demands for immigrants' full integration in the host society. Thus, this hypothesis contends that: H3the liberalization of the foreign citizens' access to Portuguese and Spanish national citizenships is fostered by the absence of anti-immigration parties in the national party systems.
A fourth hypothesis proposed by this investigation emphasises the centre-left's full commitment to multiculturalism at the public level. Multiculturalism is defined as the expression of 'modern preoccupation with identity and recognition' (Taylor 1994, 26). This research focuses on the public sphere, as recognition is related with a politics of universalism emphasising equal dignity of all individuals that involves equalisation of rights and entitlements (Joppke 2010). The primary objective involves preventing social stratification and the existence of first and second-class citizens, which can only be attained if foreign citizens have the right to become citizens. Multiculturalism can thus be associated with the framing of political claims on immigration by political actors under universal principles, with an emphasis on equality, fairness and solidarity . 2 Consequently, the last hypothesis suggests that: H4the liberalization of the foreign citizens' access to Portuguese and Spanish national citizenships is enhanced by centre-left's full commitment to multiculturalism.
The observation of this hypothesis will be assessed through a mixed-method strategy involving the analysis of political claims on immigration in the two countries conducted by secondary sources (Ros and Morales 2015; Duarte 2019), 3 the examination of the centre-left parties' political manifestos, and a basic content analysis of parliamentary debates on the nationality laws to broadly estimate the salience of perceptions of unfairness among the political elite. These analyses will be employed as an indicator of the centre-left parties' commitment to multiculturalism. As the comparative synthesis will show, the observation of the first three hypotheses in Spain failed to prompt policy liberalization, whilst the comparison with Portugal enhances the overall relevance of the last hypothesis. The next section provides the justification for the selection of the employed comparative research design.

Case selection
The present case selection of Portugal and Spain follows a most similar cases research design due to their extensive similarities and their recurrent classification as an exceptional context within the wider European context (Peixoto et al. 2012). This research strategy enhances the neutralization of common factors which can have a strong influence on national citizenship regimes (Landman 2008). First, both Iberian countries share a long history of colonialism in the South American and African continents, after they developed permanent settler colonization in those territories. 4 Consequently, both countries hold important historical relationships with third countries (Janoski 2010). Secondly, Portugal and Spain's colonial legacies, alongside the persistence of intense emigration rates, led to the presence of large national communities settled abroad. This structural pattern incentivizes both countries to reform their citizenship regimes in order to reinforce the relationship with foreign-born generations (Joppke 2010). Thirdly, largescale immigration flows were only observed in the Iberian Peninsula after the 1980s, whilst this social phenomenon developed mostly through irregular means supported by the intense demand for unskilled workers (Peixoto et al. 2012).
Whereas the timing of inflows has been quite similar in the two countries, the intensity of this social phenomenon has been distinct. Thus, the proportion of foreign citizens accounted for 9 per cent of the resident population in Spain but only 4 per cent in Portugal by 2018 (Eurobarometer 2019). Fourthly, the timing of democratization and subsequent institutionalization of liberalism was deemed crucial in past citizenship studies for understanding the tolerance towards foreign citizens (Howard 2009). Both countries share an authoritarian legacy, as Portugal and Spain became the forerunners of the third global wave of democratization in the mid-1970s through distinct paths (Gunther 2018). The last important similarity consists of the absence of anti-immigration parties in the Iberian national party systems until the 2018 Spanish regional elections (Ros and Morales 2015; Turnbull-Dugarte 2019). 5 Therefore, the mobilization of public opinion by anti-immigration parties was absent from the mainstream politics of the Iberian Peninsula until the end of the 2010s. There are salient divergences at the economic and demographic level between Portugal and Spain, but these structural factors lack a connection with policy liberalization according to past research (Howard 2009). Following this justification of the case selection, the next section explores the Portuguese case study.

Portugal
The 1974 revolution was followed by the de-colonization of newly independent African countries and the promulgation of a new Portuguese nationality law to deprive former colonial subjects of the national citizenship. Through this downsizing process, Decree Law 308/75 suppressed the 'jus soli' principle that prevailed in the past, as national citizenship was limited to those born in Portugal and those born overseas but possessing long-term residence in Portugal (Baganha and Sousa, 2005). The Law 37/81 completed this downsizing process and privileged the 'jus sanguinis' as the primary criteria regulating the acquisition of nationality at birth. Naturalization by foreign citizens depended on six years of legal residence whilst the acquisition of national citizenship by secondgeneration immigrants born inside national territory became dependent on the parents' prior regular residence for a similar period (Carvalhais 2010). This legislation recognized full tolerance towards dual nationality (Baganha and Sousa 2005).
Acquisition of Portuguese citizenship was reformed in the early 1990s by a centre-right government led by the Partido Social Democrata (PSD), after the onset of the first wave of immigration. Access to Portuguese citizenship by first-generation and second-generation immigrants became dependent on the candidates' or the parents' possession of a long-term residence authorization, at a time when most immigrants entered Portugal by irregular means (Law 25/94). Moreover, the Law 25/94 introduced a preferential treatment in favour of foreigners originating in Lusophone countries, whose first and second generations were entitled to access Portuguese nationality after a period of six years of residence. By contrast, the residence criteria imposed on immigrants of other nationalities and their descendants increased to ten years. Dual nationality continued to be fully recognized in the legislation (Table 1).
These measures derived from the centre-right government's paramount concern with limiting foreign citizens' access to Portuguese nationality and followed the 'European fortress' paradigm that was hegemonic at the European level (Carvalho 2009;Piçarra and Gil 2012). Lastly, Law 25/94 was approved by an oversized parliamentary majority including the centreright party in government, the main opposition and centre-left party (Partido Socialista) and the right-wing party (Centro Democrático e Social). In short, Portugal dropped the universal approach set in the 1980s and adopted an assimilationist model that favoured the integration of immigrants who shared the national linguistic, cultural, and religious idiosyncrasies.
Access to national citizenship resurfaced on the national political agenda due to a combination of distinct exogenous and endogenous factors. First, the centre-left Prime Minister António Guterres was actively involved in the drafting of the European Convention on Nationality. This agreement sets international standards for immigrants' access to the national citizenship and implied, for example, the suppression of the preferential treatment included in the legislation (Vink 2018). On the domestic level, the immigrant population legally settled in Portugal doubled in the early 2000s, and this trend was followed by the diversification of immigrants' origins. Consequently, the preferential system on immigrants' access to the national citizenship diverged from the increasing complexification of this social phenomenon. Lastly, immigrants' acquisition of Portuguese citizenship was hampered by the instability of the legal status of most immigrants settled in Portugal. In 2006, estimates suggested that half of the 437,000 foreign citizens settled with a regular status benefited from regularisation programmes (Peixoto et al. 2009). These trends constituted important obstacles to the second generation's acquisition of Portuguese citizenship due to their dependence on the parents' legal status, despite having been born inside national territory and lacking an effective relationship with their parents' countries of origin. The latter argument was repeated in the parliamentary debate over the new nationality law in 2006 (Piçarra and Gil 2012). Against this background, the PS electoral manifesto for the 2005 general elections pledged 'the recognition of citizenship status to those with strong linkages with Portugal, especially those individuals born in national territory who are descendants of parents born abroad' (PS 2005, 92). Following the PS's victory at this ballot, the government presented the legislation as an instrument to overturn the 'deep social unfairness' and to establish the immigrants' 'subjective right to access national citizenship' (DAR 2005).
Furthermore, the government's proposal suppressed the preferential treatment provided to immigrants originating in Lusophone countries against the demands of the PSD due to full membership of the European Convention on Nationality (DAR 2005). Remarkably, the centre-left's liberal stance followed widespread consensus among the national political elite that envisaged immigrants' access to Portuguese citizenship as a fundamental right (Carvalhais 2010). A content analysis of the parliamentary debate of the new bill suggests that injustice/unfairness were referred to 16 times by the deputies whilst equality received 11 references (DAR 2005). Accordingly, Law 2/2006 was approved by another oversized parliamentary majority including the governing parties (PS and PSD), as well as the Partido Comunista Português (PCP) and Os Verdes [The Green Party]). This law maintained 'jus sanguinis' as the primary criteria regulating the acquisition of nationality at birth, but there was a reinforcement of the 'jus soli' principle regarding the second and third generations (Table 1). This legislation established a residence-based mode for the acquisition of citizenship by immigrants' descendants born in the country, which was decoupled from the parents' residential status (Piçarra and Gil 2012; Table 1). Dual citizenship continued to be fully recognized in the legislation.
With this new legislation, Portugal abandoned the past assimilationist model and embraced a multicultural model in the mid-2000s. Regarding the proposed hypotheses concerning policy liberalization, the past relationship between Portugal and its former colonies seems to be weakly associated with the end of the preferential treatment given to immigrants originating in Lusophone countries. Secondly, the Portuguese centre-left party's incumbency coincided with the paradigm shift towards a multicultural model observed in the mid-2000s. Likewise, a positive relationship was observed between the liberalization of immigrants' acquisition of national citizenship and the lack of a relevant anti-immigration party in the national party system. Lastly, the PS's full commitment to multiculturalism in 2005 also coincides with the paradigm shift in the subsequent legislature. Considering that government actors are the most dominant in the national debates on immigration (van der Brug et al. 2015), political claims analysis suggests that the frame of universal principles was the most dominant after the PS's return to government in 2005 to the detriment of instrumental considerations (Figure 1). 6 These trends suggest that the last three explanatory factors are positively related with the observation of policy liberalization in Portugal.
The citizenship law was recently reformed by a PS minority government, after the Bloco de Esquerda (BE) presented a parliamentary proposal to grant unconditional 'jus soli' to second-generation immigrants. Following the negotiations between the left-wing parties within the parliamentary committee, Law 2/2018 expanded access to Portuguese citizenship to the second generation, but it failed to include the BE's demand (Table 1). The final draft was ratified by another oversized parliamentary majority including the centre-left party in government and the remaining left-wing parties (PCP, Os Verdes, the BE, and an animalist party named Partido Animais e Natureza), with the main opposition centre-right party (PSD) having abstained. Remarkably, the diminished political opposition to the liberalization of access to Portuguese citizenship in the late 2010s led by the CDS-PP suggests that immigration continued to be associated with universal principles by the national political elite. Furthermore, this policy development diverges from restrictive backlash observed at the European level involving the introduction of integration tests and the politicization of dual nationality (Goodman and Howard 2013). The next section will examine the Spanish model of incorporation of immigrants in the 21st century.

Spain
In Spain, immigrants' acquisition of the national citizenship is regulated by articles included in the National Constitution and the Civil Code rather than by a separate legal text (Rodriguez 2010). The 1978 constitutional text established a basic set of principles regarding the regulation of Spanish nationality, including the possibility of celebrating dual nationality agreements with Ibero-American states or other countries with special links to Spain. Consequently, extensive recognition of dual citizenship continued to be distrusted by the Spanish political elite during the democratic transition (Hazan 2014). Effectively, the 1954 reform of the civil code recognized bilateral agreements concerning dual nationality with the Ibero-American communities because it fit the narrative of Spain's perpetuation of the long-lost Spanish Empire' (Moreno Fuentes 2001). Through this reform, the Francoist regime deployed a preferential treatment of immigrants from Ibero-American countries and the Philippines. Consequently, the former foreign citizens can obtain dual nationality and naturalization after two years of legal residence whilst immigrants from other nationalities must have legal residence for a period of ten years and to renounce their nationality of origin.
In the early 1980s, a centre-left government led by the Partido Socialista Obrero Espanõl (PSOE) promoted a reform of the Civil Code but failed to operate a rupture with past policy like it was observed in Portugal. Therefore, the 1982 reform upheld 'jus sanguinis' as the guiding principle of acquisition of citizenship at birth and expanded the preferential treatment to the citizens of Andorra and Equatorial Guinea as well as to Sephardic Jews. Regarding access to Spanish citizenship by second-generation immigrants, those born inside national territory only require one year of legal residence in order to have the right to naturalize ( Table 2). The liberal regime adopted for the second generation supposes that the descendants of immigrants born in the country will more easily assimilate into their host society than those born abroad (Castles and Miller 2003).
Despite the lack of references to the third generation, the legislation granted automatic citizenship to minors, when one of the foreign parents was also born in the country. This liberal provision was justified by the intention to prevent the settlement of successive generations of foreign citizens within Spanish territory rather than by the aim of incorporating foreigners into Spanish society (Farré 2009.). Furthermore, the citizens from Andorra, Philippines, Equatorial Guinea and Portugal were exempted from the compulsory renouncement of their nationality of origin (Rodríguez 2010). Therefore, the recognition of dual citizenship also follows the preferential system that underlies immigrants' access to naturalization (Domingo and Ortera-Rivera 2015). In short, the Spanish approach to immigrants' acquisition of national citizenship from the early 1980s onwards conforms to the assimilationist model, which marks a remarkable continuity with the authoritarian past. Whereas the criteria regarding the naturalization of foreign citizens originating in former colonies is one of the most favourable among the colonial powers (Martín-Pérez and Moreno-Fuentes 2012), the general residence requirement of ten years for other foreign citizens is one of the strictest in Europe (Finotelli and La Barbera 2013).
Unlike Portugal, the Spanish legislation on immigrants' acquisition of national citizenship is characterized by strong stability. During the 1990s, a minority PSOE government introduced minor amendments, including the reduction of the residence criteria for the naturalization of refugees from ten to five years, which received overwhelming parliamentary support (only five abstentions were observed against 245 favourable votes; Cortes Generales 1990). Nonetheless, proposals presented by the Partido Nacionalista Vasco and the left-wing coalition Izquierda Unida (IU) to reduce the general residence requirement from ten to five years or to extend the preferential system to citizens of the European Community were voted down by the centre-left government, because the legislation was perceived to be 'quite liberal' (Martín-Pérez and Moreno-Fuentes 2012, 642). By contrast, when the centre-right party -Partido Popular led the government, the PSOE and the IU presented parliamentary proposals to reform immigrants' access to Spanish nationality in 1996Spanish nationality in , 1998Spanish nationality in and 1999. The centre-left party's proposals co-opted the measures proposed by the IU and PNV in the past (which were considered unnecessary at the time) but they were rejected by the PP minority government alongside the regional nationalist centre-right parties (Marín et al. 2015).
In 2002, the PP government reformed the Civil Code to reinforce the links with the emigrant community through the strengthening of 'jus sanguinis', whilst the regulations on immigrants' acquisition of national citizenship remained untouched. The PSOE's proposal to establish unconditional 'jus solis' for the second generation sought to provide equal rights and duties to the immigrant descendants, whilst the reduction of general residence criteria to five years was justified on pragmatic grounds (Cortes Generales 2002). The parliamentary debates indicating that the Spanish political elite (including members of the centre-left) perceived the national legislation as sufficiently liberal, deeming further liberalization unnecessary (Marín et al. 2015). Effectively, a content analysis of the parliamentary session concerned with the PSOE's proposal indicated that equality was referenced only once by the deputies whilst the terms of injustice/unfairness were mentioned only five times (Cortes Generales 2002). Whereas as the proposals to re-ethnicize the legislation reform received overwhelming support in parliament, the PSOE's proposal to facilitate immigrants' naturalization were rejected by the PP's absolute parliamentary majority (Marín et al. 2015).
Since the 2000s, there was a significant growth in the immigrant population settled in Spain, as the country became the third largest recipient of immigrants in the world during the 2000s (Ros and Morales 2015). By the early 2010s, immigrants from Latin America accounted only for 30 per cent of the overall foreign population (Hazan 2014). Within this context, the preferential system presents a significant barrier to the first generation of immigrants' origin in non-Hispanic countries, due to the general residency requirements and the mandatory renouncement of their original nationality (Domingo and Ortega-Rivera 2015). The PSOE's victories at the 2004 and 2008 general elections fuelled expectations of a liberal reform of Spanish nationality law, but the centre-left government failed to recover the past proposals. Effectively, the reduction of the residence criteria imposed on immigrants' naturalization was included in the PSOE's party manifesto for the 2000 general election but excluded from the similar documents presented at the , and 2011ballots (PSOE 2000, 2011. Moreover, the inaction regarding immigrants' acquisition of Spanish nationality contrasts heavily with the legislation enacted in 2007 ('Ley de Nietos') to expand the ties with the emigrant community and their descendants (Hazan 2014;Pasetti 2019).
The last significant modification regarding the immigrants' acquisition of Spanish nationality involved the PP government's introduction of a national exam to assess the candidates' knowledge of Spanish language and culture in 2015 without parliamentary debate (Finotelli and La Barbera 2017). This action included second generation immigrants and conformed with the wider restrictive backlash observed in Europe (Goodman and Howard 2013). Nonetheless, it fostered strong criticism from the PSOE, which reintroduced an overall reform of foreign citizens' access to the national citizenship for the 2015 general elections (PSOE 2015). Thereby, the PSOE acknowledged the immigrants' 'right of integration' and that acquisition of nationality represents the 'plenitude of citizenship rights' (PSOE 2015, 258). A reduction of residence criteria imposed on immigrants' naturalization and the suppression of the renouncement of nationality of origin were thus proposed by this centre-left party (PSOE 2015, 260). In 2016, the PSOE parliamentary group criticized the discrimination according immigrants' origin imposed by the current legislation and the dual system that favoured immigrants' origin in Latin American countries (The Diplomat 2016). However, policy stability persists until actuality.
In short, the Spanish citizenship paradigm has been characterized by its assimilationist nature. Regarding the relationship with the proposed hypothesis, this paradigm has been recurrently associated with path dependence effects that explain Spain's focus on the emigrant community and the preferential treatment towards colonial citizens (Martín-Pérez and Moreno-Fuentes 2012). This hypothesis seems more valuable for understanding policy stability than policy liberalization. Secondly, the centre-left's government incumbency throughout the 2000s deviates from the identified policy stability regarding immigrants' acquisition of national citizenship. A similar relationship can be observed between the lack of an anti-immigration party within the national party system until the 2018 regional elections (Ros and Morales 2015; Turnbull-Dugarte 2019) and the absence of a policy shift. By contrast, the PSOE's late commitment to multiculturalism in the mid-2010s helps to understand the lack of an overall reform since the 1980s. The analysis of political claims on immigration conducted in Spain between 1995 and 2009 indicates the overt supremacy of the instrumental frame in relation to universal principles, a trend unchanged during the PSOE's terms in government ( Figure 2). Thereby, the first and fourth hypotheses seem the most relevant to understand the policy stability observed in Spain.

Comparative synthesis
This section presents the cross-national analysis of the observations extracted from the in-depth analysis at the national level. Since the 1980s, both Iberian Nations privileged the principle of 'jus sanguinis' to regulate the automatic access to their national citizenships. However, Portugal operated a rupture with past policy, whilst a strong continuity was observed in Spain. From the early 1990s to the mid-2000s, a strong convergence towards a common assimilationist model was identified between the two countries. This model involved preferential treatment towards immigrants originating in former colonial territories over those with other nationalities. Spain adopted more liberal criteria than Portugal to regulate the second generation's access to national citizenship, whilst the preferential treatment was the most favourable among former colonial powers (Tables 1  and 2). However, dual nationality was universally recognized in Portugal since the 1980s, whilst this right is selectively recognized in Spain depending on past colonial ties in remarkable continuity with the country's authoritarian past. Against the background of the expansion of immigration into the Iberian Peninsula from the 1990s onwards, Portugal dropped the assimilationist model in favour of a multicultural paradigm in the mid-2000s, a shift which was further consolidated in 2018 (Table 1). In Spain, the parliamentary proposals presented by the IU and then the PSOE to water-down the assimilationist paradigm observed in the 1990s and early 2000s were unsuccessful. These trends reflected the opposition of the PSOE and then the PP governments because the legislation was perceived as being sufficiently liberal and not problematic. Moreover, the PSOE's government incumbency during the 2000s failed to promote a paradigm shift regarding foreign citizens' access to national citizenship, in contrast to what occurred following the PS victory at the 2005 legislative elections in Portugal. The policy developments observed in the 2010s also suggest that Portugal deviated from the restrictive backlash observed in Europe, whilst Spain's conformed to the trend observed in other European counterparts. Notwithstanding the pressures at the international and domestic levels, Portugal and Spain failed to converge from the mid-2000s onwards regarding their national policies on immigrants' acquisition of national citizenship.
The comparative analysis suggests that path dependence effects were closely associated with the paradigm stability in Spain but diverged from the policy shift in Portugal. Therefore, past colonial ties do not explain the policy liberalisation observed in the Iberian Peninsula. Secondly, the PS's government incumbency coincided with the paradigm shift observed in Portugal, whilst the PSOE's two terms in office during the 2000s failed to result in a similar outcome in Spain. Thirdly, the absence of anti-immigration parties in the national party systems until 2019 coincides with the policy liberalisation in Portugal in the mid-2000s but deviates from the paradigm stability in its Iberian counterpart. Thus, the Portuguese case study suggests that party governments' ideological positioning and the absence of anti-immigration parties may be necessary causal factors behind policy liberalisations, but were insufficient to provoke this political process in Spain. To explain the identified cross-national policy variation in the context of widespread similarities, this investigation suggests that the role of ideas among the centre-left parties should be explored (Bleich 2003;Hay and Gofas 2010).
Regarding the fourth hypothesis, the PS's commitment to multiculturalism at the 2005 general elections coincides with the subsequent policy liberalisation and the dropping of the assimilationist model. In Spain, the absence of a similar process, until the PSOE's adoption of multiculturalism in the mid-2010s, coincides with the stability of the assimilationist paradigm from the 1980s onwards. Political claims analysis in the period of the centre-left's government incumbency in Portugal during the 2000s highlights the hegemony of political claims framed by universal principles, whilst the Spanish political debate was mainly dominated by instrumental justifications and feeble references to full equality (Figures 1 and 2). A similar relationship can be found in the analysis of the parliamentary debates concerning immigrants' acquisition of national citizenship, as references to unfairness and equality were more salient in Portugal than in Spain. Lastly, the reform of immigrants' access to national citizenship was excluded from the PSOE's electoral manifestos from 2000 to 2015. These trends suggest that the preferential treatment towards Hispanic immigrants was not perceived as problematic by the Spanish centre-left until the mid-2010s.
Therefore, the Portuguese case study suggests that the centre-left's commitment to multiculturalism seems to be a necessary condition for policy liberalisation but looks insufficient to prompt this political process, unless it is observed in conjunction with these parties' government incumbency in the absence of anti-immigration parties. Further research is required to understand the distinct approaches of the Portuguese and Spanish centre-left parties to immigrants' acquisition of national citizenship.
Considering utilitarian perspectives, the Spanish centre-left should have higher incentives than its Iberian counterpart to enfranchise the larger immigrant community and capitalize on their electoral support (Koopmans 2013). Another potential explanatory factor relates to public concern with immigration, as this topic featured among the issues of greatest importance to the Spanish electorate, in contrast to its lack of salience in Portugal (Ec.europa.eu 2019). According to secondary sources, the pressure of civil society organisations on this topic was weak in both nations (Carvalhais 2010;Ros and Morales 2015). From a political competition perspective, the ideological shifts within the centre-left parties might be related with the emergence of radical-left competitors such as the BE in Portugal in the late 1990s and Podemos in Spain in the mid-2010s.

Conclusions
A policy convergence towards the adoption of an assimilationist model was identified between the Iberian countries from the early 1990s to the mid-2000s. This trend was associated with endogenous factors related with path dependence effects derived from the selected countries' colonial legacy. Nevertheless, Portugal dropped the preferential treatment granted to former colonial citizens in favour of universal access for foreign citizens' acquisition of national citizenship in the mid-2000s. By contrast, Spain remains attached to the assimilationist model set in the early 1980s through the maintenance of the preferential system favouring foreign citizens from Hispanic countries, as well as the selective acceptance of dual citizenship. This divergence was strengthened by the policy developments observed in the 2010s, as Portugal's approach deviated from the wider restrictive backlash observed in Europe unlike Spain's. Consequently, this research confirms that variation across Europe regarding foreign citizens' acquisition of national citizenships continues to be acute. In the twenty-first century, European states like Spain continue to uphold assimilationist models that enhance the perception of an important contingent of the foreign population as second-class citizens, whose access to full citizenship is overtly hindered by the legislation.
Secondly, this comparative research highlights the contingency of political liberalisation of immigrants' acquisition of national citizenship. The Spanish case study suggests that centre-left parties' government incumbency and the absence of antiimmigration parties were not sufficient to prompt the liberalization of immigrants' acquisition of national citizenship. By contrast, the Portuguese experience suggests that these causal factors operated in conjunction with the mainstream centre-left party's commitment to multiculturalism in the mid-2000s, an intra-party shift which was only observed a decade later in the PSOE. Thus, the salience of the centre left parties' commitment to multiculturalism and the promotion of full equality was enhanced by the cross-national analysis relative to the other proposed causal factors. Considering the ascension of an anti-immigration party named VOX to the Spanish national party system following the 2018 regional elections, policy liberalization in Spain seems more unlikely in the short-term, and the divergences between the Iberian nations will persist in the coming decade. Lastly, further research should explore the motives behind the variations in the centre-left parties' commitment to multiculturalism and its repercussions on their proposals concerning foreign citizens' acquisition of national citizenship. Notes 1. Past research involving multivariate analysis over 15 EU member-states concluded there was a lack of relationship between policy liberalization and economic factors (GDP per capita, rates of unemployment) or demographic factors (absolute number of immigrants settled in the countries, the proportion of immigrants within the overall population; see Howard 2009, 65) 2. This comparative research evaluates arguments that actors employ to justify their positions on immigration, and assesses the observation of two other frames: instrumental (when a political stance is presented as a rational choice, based on the calculation of utility) and identity (when a particular positions is justified on the basis of cultural differences between migrants and the host society) (van der Brug et al. 2015, 29). 3. The analysis of political claims concerning immigration in Spain and Portugal randomly selected 700 days for each country between 1995 and 2014, and all articles about immigration were sampled from two national newspapers (Ros and Morales 2015; Duarte 2019). A political claim consists of a purposive statement or action by a collective actor that affects the interests of immigrants, and a single article can contain multiple claims . Each claim was coded according to a common codebook, which includes the analysis of political frames. 4. Spain continues to hold two enclaves on the northern Mediterranean coast formed by Ceuta and Melilla, which are targets for irregular immigration (Magone 2008). 5. Nonetheless, Alonso and Kaltwasser (2015) associated the weakness of radical right parties in Spain with the Partido Popular government's (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) employment of nationalism and immigration as valence issues in this party's electoral strategy. In the early 2000s, it was stated that: 'Prime Minister Aznar made anti-immigrant sentiment a respectable element of mainstream political discourse in Spain' (Cornelius 2004, 392) 6. Political claims analysis on immigration conducted between 1995 and 2014 highlights the dominance of the frame of universal principles between 2009 and 2013. In 2014, the proportion of political claims framed by instrumental considerations was slightly higher than those associated with universal principles (Duarte 2018).