Multiple citizenship
Multiple citizenship, also known as dual or multiple nationality, refers to the legal status in which an individual is recognized as a citizen by two or more sovereign states simultaneously, entailing rights and obligations toward each.[1][2] Countries establish their own nationality laws governing whether multiple citizenship is permitted, with policies ranging from full allowance to outright prohibition or conditional acceptance upon renunciation of prior nationalities.[1] The United States, for instance, recognizes multiple citizenship but asserts primary allegiance from its nationals and does not formally encourage the practice.[3] This status arises commonly through birthright citizenship (jus soli or jus sanguinis), marriage, naturalization, or investment programs, and has become more prevalent amid global migration and interconnected economies.[4] While conferring advantages such as enhanced travel mobility via multiple passports, access to diverse job markets, and inheritance rights across borders, multiple citizenship imposes dual fiscal responsibilities, including potential taxation on worldwide income by countries like the United States regardless of residence.[5][6] Significant challenges include conflicting military service obligations, where dual nationals may face conscription demands from multiple states, and diplomatic vulnerabilities, as one country's protection might not extend fully in another's jurisdiction.[3][7] Historically viewed with suspicion for risking divided loyalties—likened to "self-evident absurdity" in early 20th-century discourse—multiple citizenship persists amid debates over national security and sovereignty, particularly in contexts of espionage or wartime allegiance.[8][7] Despite these tensions, acceptance has grown, with many nations now permitting it to retain ties with emigrants and attract skilled migrants.[9]Conceptual Foundations
Definition and Core Concepts
Multiple citizenship, interchangeably termed dual citizenship, plural citizenship, or dual nationality, refers to the legal status in which an individual is simultaneously recognized as a citizen by two or more sovereign states.[1] This condition stems from the autonomous nationality laws of each involved country, which independently determine citizenship eligibility through mechanisms such as birthright (jus soli or jus sanguinis), descent, naturalization, or marriage, without mandating the forfeiture of existing citizenships.[2] As of 2022, approximately 75% of countries worldwide permit some form of multiple citizenship, though policies vary, with full reciprocity between states being rare.[2] At its core, multiple citizenship entails a dual set of rights and obligations, potentially amplifying personal opportunities while introducing compliance complexities. Rights may include access to multiple passports for travel, eligibility for social services, property ownership, and political participation like voting in each nation's elections, subject to residency requirements.[3] Obligations, however, extend to fulfilling legal duties in all jurisdictions, such as income tax reporting on worldwide earnings in high-tax countries like the United States, irrespective of residence, or mandatory military service where applicable, as seen in nations like Israel or South Korea for dual nationals.[3] Dual nationals must often use the passport of the destination country for entry and exit to avoid diplomatic issues, underscoring the practical interplay of state sovereignty over nationals abroad.[1] A fundamental tension in multiple citizenship arises from the principle of exclusive allegiance historically embedded in international law, such as the 1930 Hague Convention's preference for singular nationality to prevent statelessness or conflicting loyalties.[1] While modern practice accommodates multiplicity for pragmatic reasons like global mobility and family ties, it can lead to conflicts during wartime, extradition disputes, or security clearances, where one state's claims may supersede another's.[3] The United States recognizes multiple citizenship de facto, derived from the 14th Amendment's birthright clause and naturalization statutes, but does not actively promote it and requires naturalizing immigrants to swear an oath renouncing prior allegiances, though enforcement of renunciation remains unenforced in practice.[4][1]Legal Principles Underpinning Citizenship Multiplicity
The legal status of multiple citizenship rests on the principle of state sovereignty in defining nationality, whereby each sovereign state holds exclusive competence to establish criteria for acquiring, retaining, or losing its nationality, without international law imposing a general duty to prohibit or permit multiplicity.[10] This sovereignty, rooted in customary international law, allows states to enact domestic laws tolerating dual or multiple nationalities—such as through jus soli (birth on territory) or jus sanguinis (descent)—while others impose restrictions, like mandatory renunciation upon naturalization, to avoid divided loyalties.[11] Conflicts arise when an individual's multiple nationalities lead to competing claims of allegiance, prompting international principles to prioritize factual ties over formal status. To address such conflicts, the doctrine of effective nationality or dominant nationality serves as a customary rule, requiring assessment of an individual's genuine connection to a state—evaluated by factors including habitual residence, center of interests, family ties, participation in public life, and diplomatic protection history—rather than mere legal attribution.[12] This principle, articulated by the International Court of Justice in the 1955 Nottebohm case (Liechtenstein v. Guatemala), holds that nationality must reflect a "genuine link" for purposes like diplomatic protection, barring a state from espousing a claim against another state of which the individual is also a national unless their dominant ties lie with the claimant state.[10] In practice, this resolves issues in extradition, military service obligations, and taxation, where the state of effective nationality exercises precedence; for instance, arbitral tribunals under investment treaties apply it to determine investor eligibility, disqualifying dual nationals whose dominant links are to the respondent state.[13] Early 20th-century efforts sought to curtail multiple citizenship to prevent statelessness and allegiance conflicts, as embodied in the 1930 Hague Convention on Certain Questions Relating to the Conflict of Nationality Laws, which urged states to avoid dual acquisition at birth (e.g., via parental option to elect one nationality) and required adults with multiple nationalities to choose one upon reaching majority, with third states recognizing only the retained nationality in international dealings.[14] Ratified by only 20 states and lacking provisions for enforcement, the Convention failed to establish a binding norm against multiplicity, influencing few modern policies and yielding to sovereign discretion.[10] Subsequent frameworks reflect greater tolerance for multiple citizenship, balancing sovereignty with obligations to prevent arbitrary statelessness under the 1954 UN Convention Relating to the Status of Stateless Persons and the 1961 UN Convention on the Reduction of Statelessness, which indirectly accommodate dual nationality by prohibiting deprivation that creates statelessness absent voluntary renunciation.[15] Regionally, the 1997 European Convention on Nationality marks a shift by defining multiple nationality and permitting it without mandatory renunciation in cases like naturalization or marriage, while allowing states to limit it domestically (e.g., for public office holders) and regulating military obligations to the state of dominant residence.[16] As of 2023, 21 Council of Europe states have ratified it, promoting consistency in Europe where over 80% of countries now allow dual citizenship for adults. These principles underscore that while multiple citizenship imposes no inherent international prohibition, states must navigate resultant obligations through effective nationality assessments to uphold causal accountability in cross-border relations.[11]Historical Evolution
Ancient and Pre-Modern Practices
In ancient Greek city-states, such as Athens and Sparta, citizenship was an exclusive status confined to a single polis, acquired primarily through paternal descent from existing citizens and requiring active participation in civic life. Free adult males meeting these criteria enjoyed rights like assembly participation and legal protections, while women, slaves, and metics—resident foreigners from other poleis—were excluded; metics paid special taxes and could not own property or vote, underscoring the singular allegiance demanded.[17] No formal mechanism existed for multiple citizenships, as shifting loyalty to another polis typically required renunciation of the original, a rare occurrence granted only by exceptional decree.[18] The Roman Republic introduced greater flexibility, particularly after the Social War (91–88 BCE), when citizenship (civitas Romana) was extended to Italian allies via the lex Julia, allowing them to retain local municipal citizenships alongside Roman status. This dual arrangement preserved provincial civic institutions and rights, such as local magistracies, while subordinating them to Roman authority; for instance, the Apostle Paul held both Roman citizenship and that of Tarsus, a Hellenistic city, enabling him to invoke protections from both. By the 1st century BCE, this practice was institutionalized, distinguishing Rome from Greek exclusivity and facilitating imperial integration, though full equality remained limited until the Edict of Caracalla in 212 CE extended citizenship empire-wide without necessarily abolishing local statuses.[19] In the Graeco-Roman East, elites often navigated multiple civic identities, with poleis granting honorary citizenships compatible with Roman, though primary fiscal and military obligations favored the imperial center.[20] In medieval Europe, citizenship shifted toward urban communes and guilds, emphasizing oaths of fidelity to specific cities rather than expansive states; residents could acquire multiple urban citizenships through prolonged residence, economic contributions, or purchase, as seen in Italian city-states like Venice or Florence, where merchants held statuses in trade networks spanning regions. However, these were pragmatic, non-exclusive affiliations tied to privileges like market access and legal recourse, not undivided national loyalty, amid fragmented feudal structures where overlords and ecclesiastical ties created layered allegiances. Pre-modern practices thus tolerated overlapping civic ties in multi-jurisdictional empires like the Holy Roman Empire, but formal multiple nationality—as a state-level status—remained undeveloped until the rise of sovereign nation-states in the 18th century, when singular allegiance became a diplomatic norm.19th and 20th Century Shifts
In the nineteenth century, the consolidation of sovereign nation-states prompted a doctrinal shift from perpetual allegiance—under which citizenship was lifelong and irrevocable—to elective citizenship, allowing individuals to renounce original nationality upon acquiring a foreign one. This transition, evident in Britain's Naturalisation Act of 1870, which permitted expatriation but automatically revoked British citizenship for those naturalizing abroad, reflected concerns over divided loyalties amid rising interstate rivalries and emigration waves.[21] Similarly, the United States affirmed expatriation rights through the Expatriation Act of 1868, following diplomatic disputes like the 1863 "Trent Affair" involving dual nationals, yet dual citizenship persisted inadvertently through combinations of jus soli (birthright by soil) and jus sanguinis (descent-based) rules.[8] Governments viewed multiple nationalities as a threat to exclusive allegiance, particularly for military service, leading to policies that penalized dual status, such as automatic denaturalization upon foreign enlistment or voting.[10] These measures aligned with an international consensus against dual nationality to avert diplomatic conflicts, as states feared "hyphenated" citizens might claim protections from multiple governments while owing obligations to adversaries. By the late nineteenth century, over 20 bilateral treaties, including the 1868 U.S.-North German Confederation agreement, sought to clarify expatriation and reduce dual status by recognizing naturalization abroad as terminating prior citizenship.[22] However, enforcement varied; France and Italy tolerated limited dual citizenship for minors but required choice upon majority, while empires like Austria-Hungary grappled with ethnic minorities holding overlapping claims.[23] The era's mass migrations—numbering 36 million Europeans to the Americas between 1870 and 1914—intensified these tensions, as returnees or children born abroad invoked conflicting claims, prompting statutes like Germany's 1871 Reich Nationality Law, which mandated loss of citizenship upon foreign naturalization unless explicitly retained.[24] Entering the twentieth century, world wars amplified aversion to dual nationality, with over 100,000 U.S. dual citizens facing conscription dilemmas in 1917–1918, leading to the 1907 U.S. Expatriation Act provisions stripping citizenship from women marrying foreigners.[8] The 1930 Hague Convention on Certain Questions Relating to the Conflict of Nationality Laws, ratified by 20 states, urged minimizing dual nationality through rules favoring the nationality of habitual residence and requiring choice at majority, but its limited adoption—due to sovereignty assertions—failed to curb the practice.[10] Post-1945 decolonization and labor migrations shifted priorities; Britain’s 1948 British Nationality Act permitted dual citizenship for Commonwealth citizens without mandatory renunciation, accommodating 800 million subjects transitioning to independence.[22] By the 1960s, economic imperatives and family unification policies eroded prohibitions: the U.S. Supreme Court’s 1967 Afroyim v. Rusk decision (5–4) barred involuntary loss of citizenship except for fraud, protecting dual status as a constitutional right, while countries like Mexico (1978 reform) and Australia (1986) began allowing retention for emigrants' descendants.[24] This gradual liberalization, driven by globalization and remittances exceeding $700 billion annually by 2000, marked a pragmatic acceptance of multiple ties, though security concerns persisted in restricting dual nationals from sensitive offices.[21]Post-2000 Developments and Policy Reversals
Following the liberalization trends of the late 20th century, the period after 2000 saw further expansions of multiple citizenship policies in numerous countries, driven by aims to enhance immigrant integration, attract skilled migrants, and strengthen economic links with diasporas through remittances and investment. Empirical data indicate that such reforms correlated with increased naturalization rates; for instance, Germany's 2000 citizenship law reform, which permitted dual citizenship for children born in the country to long-term foreign residents, resulted in a sustained uptick in citizenship acquisitions without evidence that restricting adult dual nationality deterred applications.[25] Similarly, Latin American nations like Brazil and Colombia, building on 1990s reforms, codified dual citizenship rights post-2000 to re-engage emigrants, enabling voting and property rights abroad while retaining origin-country ties.[9] Australia enacted a pivotal change on April 4, 2002, by repealing Section 17 of the Australian Citizenship Act 1948, which had previously caused automatic loss of Australian citizenship upon voluntary acquisition of another nationality. This reversal of prior exclusivity aligned with globalization pressures, allowing over 4 million Australians holding foreign passports to retain full rights without renunciation.[26][27] The Philippines followed with Republic Act No. 9225 on August 29, 2003, the Citizenship Retention and Re-acquisition Act, permitting natural-born Filipinos who had naturalized abroad to reacquire Philippine citizenship without forfeiting their foreign one, thereby formalizing dual status for an estimated 10 million overseas workers and their descendants to facilitate return migration and economic contributions.[28][29] Germany's trajectory exemplifies iterative policy evolution, with the 2000 reform's conditional dual allowance for jus soli births giving way to the June 27, 2024, Act on the Modernization of Citizenship Law, which eliminated renunciation requirements for naturalized adults and shortened residency periods, reflecting empirical recognition that prior restrictions hindered integration amid labor shortages.[30][31] In contrast, reversals or tightenings were less common but occurred in contexts of security and integration concerns; the Netherlands, after briefly easing in the 1990s, reinforced post-2000 its default rule mandating renunciation of prior citizenship upon naturalization, except for EU/EEA/Swiss nationals or refugees, to prioritize singular allegiance, though exceptions have proliferated amid practical enforcement challenges.[32][33] Post-9/11 securitization prompted debates on dual loyalty in several states, yet few outright bans emerged where allowances existed; instead, functional restrictions proliferated, such as barring dual citizens from certain public offices in countries like Armenia and Egypt.[34] Italy's April 2025 decree limited jus sanguinis claims to descendants of emigrants after February 27, 1948, curtailing automatic multiple acquisitions via distant ancestry to curb administrative overload from over 60,000 annual applications, though existing dual statuses remain unaffected.[35] These adjustments underscore causal tensions between openness for economic gain and safeguards against divided allegiances, with data showing permissive policies boosting fiscal inflows but occasionally straining welfare systems in high-immigration contexts.[36]Mechanisms of Acquisition and Retention
Automatic Acquisition via Birth or Descent
Multiple citizenship is automatically acquired through jus sanguinis, the principle conferring nationality based on descent from citizen parent(s), when parents hold citizenships from different countries that both transmit rights at birth. This occurs irrespective of the child's birthplace, as long as each parent's country recognizes the descent claim without immediate renunciation requirements. For instance, a child born to one Italian parent acquires Italian citizenship by birth under Law No. 91 of 1992, which explicitly permits holding multiple citizenships simultaneously.[37] Similarly, under French nationality law, citizenship passes to children of at least one French parent born abroad, often resulting in dual status alongside the other parent's nationality if compatible. In Germany, since the Nationality Act of 2000, children born to foreign parents may acquire German citizenship by descent if a parent has legally resided for eight years, but pure jus sanguinis applies for German citizen parents, enabling multiple nationalities from birth without prohibition for minors. The jus soli principle, granting citizenship by birthplace, leads to automatic multiple citizenship in countries with unconditional application when combined with parental descent rights. In the United States, the Fourteenth Amendment, ratified on July 9, 1868, provides that "all persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens," applying to children of non-citizen parents (except diplomats), who retain any foreign citizenship acquired by descent. U.S. law, per the Immigration and Nationality Act (8 U.S.C. § 1401), accommodates dual nationality at birth without requiring relinquishment.[38] Canada follows suit, with Section 3(1)(a) of the Citizenship Act granting citizenship to those born in Canada, while permitting multiple citizenships explicitly since amendments in 1977.[39] This overlap frequently produces dual or triple citizenship; for example, a child born in Canada to U.S. and Italian parents receives Canadian citizenship by soil, U.S. by descent (if a parent meets transmission criteria), and Italian by descent.[40] In Latin America, unrestricted jus soli predominates, with countries like Brazil (Constitution of 1988, Article 12), Argentina (Constitution of 1853, Article 75), and Mexico granting automatic citizenship at birth on territory, often alongside parental nationalities since most allow dual status. Approximately 33 countries worldwide apply unconditional jus soli as of 2025, primarily in the Americas, facilitating multiple citizenship when parents transmit foreign rights.[41] These mechanisms reflect historical shifts toward inclusive nationality laws, though some nations impose later choices upon majority if dual is disallowed, the initial acquisition remains automatic.[42]Acquired Through Naturalization, Marriage, or Investment
![Naturalization residence requirements by country][float-right]
Naturalization typically requires a period of lawful residency, language proficiency, and oaths of allegiance, with outcomes for multiple citizenship varying by the naturalizing and origin countries' laws. In the United States, naturalization does not mandate renunciation of prior nationalities, permitting dual or multiple citizenship provided the origin country recognizes it.[1] Similarly, Canada and Australia allow multiple citizenship upon naturalization without requiring renunciation.[43] In contrast, countries like China, India, and Japan prohibit multiple citizenship, compelling applicants to renounce prior nationalities during naturalization.[44] Germany reformed its policy effective June 27, 2024, to permit dual citizenship for naturalized immigrants in most cases, reversing prior restrictions that often required renunciation except for EU or Swiss citizens.[45]
Citizenship through marriage often accelerates naturalization timelines for spouses of citizens, facilitating multiple citizenship where permitted. In the United States, spouses of U.S. citizens can apply for naturalization after three years of permanent residency (versus five for others), retaining origin citizenship if allowed by both nations.[46] Brazil grants citizenship to foreign spouses after one year of marriage and residency, explicitly allowing dual nationality.[47] Spain offers naturalization after one year of legal residency for spouses, with dual citizenship permitted for certain Latin American origin countries but requiring renunciation otherwise.[47] Israel provides expedited citizenship to spouses under the Law of Return, compatible with dual status.[47] However, acquisition is not automatic and demands proof of genuine marriage to avoid fraud scrutiny.[48]
Citizenship by investment (CBI) programs enable multiple citizenship through financial contributions, real estate, or bonds, with most explicitly permitting retention of prior nationalities. Caribbean nations dominate this field: Antigua and Barbuda requires a minimum $230,000 non-refundable contribution or $400,000 real estate investment, processing applications in 3-4 months.[49] St. Kitts and Nevis, operational since 1984, mandates $250,000 contributions for a single applicant, offering visa-free access to over 150 countries.[50] Grenada accepts $235,000 donations, uniquely providing E-2 visa eligibility for U.S. investment.[51] Beyond the Caribbean, Turkey's program demands $400,000 real estate for citizenship in 3-6 months, allowing dual.[52] Vanuatu offers passports via $130,000 donations, processed in 1-2 months.[52] Nauru launched its CBI in 2024 with no residency requirement and full dual citizenship support.[49] These programs face criticism for potential security risks but adhere to due diligence standards set by organizations like the Investment Migration Council.[53]
| Program | Minimum Investment | Processing Time | Dual Citizenship Allowed |
|---|---|---|---|
| Antigua and Barbuda | $230,000 contribution | 3-4 months | Yes[49] |
| St. Kitts and Nevis | $250,000 contribution | 3-6 months | Yes[50] |
| Grenada | $235,000 contribution | 4-6 months | Yes[51] |
| Turkey | $400,000 real estate | 3-6 months | Yes[52] |
| Vanuatu | $130,000 donation | 1-2 months | Yes[52] |
Restrictions, Renunciation, and Forced Loss
Several countries maintain strict restrictions on multiple citizenship to prioritize national loyalty and security, often requiring applicants for naturalization to renounce prior nationalities or imposing automatic forfeiture upon acquisition of a foreign one. China's Nationality Law of 1980, as amended, explicitly bars dual nationality in Article 3, mandating that any Chinese national who voluntarily acquires foreign citizenship loses Chinese nationality automatically under Article 9, with no recognition of retained ties. India similarly prohibits dual citizenship for adults under the Citizenship Act of 1955, as amended, offering Overseas Citizenship of India status as a lifelong visa-like alternative but requiring formal renunciation of Indian citizenship to naturalize elsewhere, with penalties for concealment including fines up to 10,000 rupees or imprisonment.[44] In Japan, the Nationality Law requires renunciation of foreign citizenship upon reaching adulthood for dual nationals or mandates loss upon voluntary foreign naturalization, enforced through notifications to authorities.[55] European nations exhibit varied restrictions, often tied to naturalization processes. Austria's Nationality Act generally demands renunciation of prior citizenships for naturalization, with limited exceptions for those born with dual status or via descent from Austrian emigrants, as confirmed in 2024 policy updates.[56] The Netherlands requires renunciation unless the applicant holds citizenship from certain countries like former colonies or via special ministerial discretion, reflecting concerns over integration and allegiance.[56] These policies stem from historical fears of divided loyalties, particularly in security-sensitive roles, though empirical data on loyalty risks from multiple citizenship remains sparse and contested, with no large-scale studies linking it causally to higher treason rates compared to single nationals. Voluntary renunciation of citizenship, frequently pursued to comply with restrictive policies or alleviate dual obligations like taxation, follows formalized procedures varying by jurisdiction. In the United States, under 8 U.S.C. § 1481(a)(6), individuals must appear personally before a U.S. consular or diplomatic officer abroad, swear an oath of renunciation with intent to relinquish, and pay a $2,350 fee as of 2024, after which a Certificate of Loss of Nationality is issued, though tax liabilities under the Reed Amendment may apply for those deemed tax evaders.[57] South Africa's Citizenship Act allows renunciation only after acquiring another citizenship, requiring submission of Form BI-1664 to the Department of Home Affairs along with proof of alternative nationality and a R350 fee, effective upon ministerial approval to prevent statelessness.[58] In the European Union, countries like Germany permit renunciation via declaration to authorities if the individual holds or will acquire another nationality, but Austria restricts it to those residing abroad, ensuring no resulting statelessness per the 1961 UN Convention.[59] These processes underscore causal incentives: renunciation often enables access to otherwise barred opportunities, such as naturalization in restrictive states, but irreversible effects like loss of inheritance rights or consular protection highlight the gravity of the decision. Forced or involuntary loss of citizenship arises primarily through automatic mechanisms triggered by prohibited acts or judicial denaturalization for procurement irregularities, particularly relevant in multiple citizenship contexts where foreign naturalization violates exclusivity rules. Under U.S. law, 8 U.S.C. § 1481(a)(2) provides for loss via voluntary naturalization in a foreign state through an oath of allegiance, but only if accompanied by intent to relinquish U.S. citizenship, as clarified in Afroyim v. Rusk (1967) and subsequent cases; mere acquisition of dual status without expatriating intent does not trigger forfeiture.[60] Denaturalization for fraud, per 8 U.S.C. § 1451, targets concealment of material facts like criminal convictions during naturalization, with the Department of Justice revoking citizenship in 94 cases from 2009-2018, escalating to priorities for terrorism-linked fraud post-2025.[61] In nations prohibiting multiples, such as China, foreign naturalization directly causes automatic loss without judicial process, enforced administratively to uphold unitary allegiance. Other grounds include disloyalty acts, like serving in a foreign military against the state's interests, leading to revocation in countries like the UK under the British Nationality Act 1981 for national security threats, as in 2020-2024 cases involving ISIS affiliates where 20+ citizenships were stripped. These measures reflect realist assessments of risk, prioritizing empirical threats from divided allegiances over abstract rights claims, though international law via the 1961 Convention limits application to avoid statelessness.[62]International Legal Frameworks
Dominant and Effective Nationality Doctrines
The doctrines of dominant and effective nationality serve as mechanisms in international law to ascertain the prevailing nationality among multiple citizenships held by an individual, particularly in contexts such as diplomatic protection and state responsibility. These principles prioritize factual connections over mere formal acquisition, ensuring that nationality reflects a genuine link between the individual and the state for purposes of international claims. They emerged as responses to the increasing prevalence of dual or multiple nationalities, aiming to prevent abuse in interstate disputes.[12] The principle of effective nationality was articulated by the International Court of Justice (ICJ) in the Nottebohm case (Liechtenstein v. Guatemala, judgment of April 6, 1955), where the Court ruled that naturalization conferring nationality must demonstrate a real and effective connection, such as habitual residence, center of interests, or family ties, rather than serving solely as a pretext for diplomatic protection. In that case, Friedrich Nottebohm, a German national residing primarily in Guatemala, acquired Liechtenstein citizenship in 1939 without substantial ties to Liechtenstein; the ICJ held that Guatemala was not obligated to recognize this nationality for protection claims against it, as it lacked genuine effectiveness compared to his Guatemalan residence and business interests. This established effective nationality as a requirement for third states to respect a claimant state's assertion of diplomatic protection, emphasizing factual bonds over nominal status.[63] The doctrine of dominant nationality complements effective nationality specifically for individuals with dual or multiple citizenships involving the respondent state, determining which nationality predominates based on the strength of ties to each state. Factors considered include the individual's predominant residence, participation in public life, military service, taxation, and intent as evidenced by declarations or conduct; for instance, longer-term residence and economic interests in one state may render that nationality dominant. This approach, rooted in customary international law and reflected in the 1930 Hague Convention on Certain Questions Relating to the Conflict of Nationality Laws (Article 5), allows the state of dominant nationality to exercise protection against third states but bars claims against the state of the individual's other nationality, as affirmed in arbitral practice such as the Merge claim (United States v. Italy, 1955). Tribunals apply it discretionarily, weighing evidence holistically rather than mechanically.[64][65] In modern applications, such as investor-state arbitration under treaties like the ICSID Convention or bilateral investment treaties, tribunals invoke dominant and effective nationality to assess standing for dual nationals, often rejecting claims where the investor's dominant ties lie with the respondent state, as in Champion Trading Co. v. Egypt (2006), where U.S.-Egyptian dual nationals were denied protection due to predominant Egyptian connections. These doctrines underscore a causal realism in nationality attribution: formal multiple citizenships do not equate to equal international efficacy, with empirical ties dictating enforceability to avoid opportunistic assertions. However, their scope remains debated, as some treaties explicitly exclude dual nationals or limit the doctrines' application, reflecting varying state practices amid rising multiple citizenships.[12][65]Supranational and Regional Arrangements
The European Union (EU) represents a primary supranational framework addressing aspects of multiple citizenship through its layered citizenship model. Established by the Maastricht Treaty on European Union, effective November 1, 1993, EU citizenship is automatically conferred upon individuals holding the nationality of any EU member state, granting supranational rights such as freedom of movement, residence, and participation in European Parliament elections irrespective of national restrictions on dual nationality. This arrangement does not harmonize member states' policies on multiple nationality, which remain a national competence under Article 9 of the Treaty on European Union; thus, while EU citizenship supplements national ones without requiring renunciation, countries like Austria and the Netherlands generally prohibit dual nationality for naturalized citizens, whereas others like France and Italy permit it broadly.[66] The European Court of Justice has upheld that EU law prevails in cases where national rules conflict with EU rights, as in the 2007 Micheletti case affirming Spain's recognition of dual EU/non-EU nationality. The Council of Europe, a regional organization distinct from the EU, has shaped multiple nationality through conventions emphasizing reduction or tolerance based on evolving state practices. The 1963 Convention on the Reduction of Cases of Multiple Nationality and Military Obligations in Cases of Multiple Nationality, ratified by 20 states including France (1964) and Germany (1999), mandates renunciation of prior nationality upon naturalization and prohibits automatic acquisition of multiple nationality by children of binational parents unless retained until age 18 or 23.[67] However, its limited ratifications and a 1993 protocol allowing voluntary multiple nationality reflect declining adherence, as many signatories have since liberalized policies amid migration pressures. In contrast, the 1997 European Convention on Nationality, ratified by 22 Council of Europe members as of 2023, permits states to allow multiple nationality without restriction, prohibits arbitrary deprivation leading to multiple nationality, and prioritizes avoidance of statelessness, influencing reforms in countries like the United Kingdom (1981 British Nationality Act amendments). These instruments underscore a causal shift from post-World War II concerns over loyalty and military service to pragmatic acceptance of multiple allegiances in diverse societies. Beyond Europe, regional arrangements in other continents facilitate multiple citizenship indirectly through mobility and naturalization pathways rather than supranational citizenship. The Southern Common Market (Mercosur), via its 2002 Agreement on Residence for Nationals of Mercosur States, enables citizens of member states (Argentina, Brazil, Paraguay, Uruguay) and associates (e.g., Bolivia) to obtain temporary residence for up to two years, renewable and convertible to permanent status, often leading to naturalized citizenship without mandatory renunciation in permissive members like Argentina. This has processed over 100,000 applications annually by 2015, enhancing regional integration without overriding national dual nationality laws, which vary (e.g., Brazil allows it since 1994).[68] In Africa, the African Union (AU) lacks a unified citizenship but advanced compatibility via the 2014 Protocol to the African Charter on Human and Peoples' Rights on the Rights of Older Persons and related nationality protocols; however, the 2006 African Charter on Democracy, Elections and Governance (ratified by 35 states as of 2023) implicitly supports dual nationality by prohibiting discrimination based on it, contributing to policy shifts in 28 AU members permitting it by acquisition or descent as of 2020.[69] These frameworks prioritize economic mobility and diaspora engagement over strict singularity, though enforcement varies due to national sovereignty.[70]Conflicts in International Law and Treaties
International law encounters persistent conflicts with multiple nationality due to the absence of uniform rules on acquisition and the sovereign right of states to determine their nationals, often resulting in overlapping claims of allegiance and protection. Customary international law prohibits a state from exercising diplomatic protection on behalf of one of its nationals against another state of which that person is also a national, as the individual cannot invoke protection from one sovereign while bound by allegiance to the respondent state.[71][72] This principle stems from the Vattel-inspired doctrine that states protect their own subjects abroad but refrain from interfering in internal matters of another sovereign to which the person owes duties.[73] The 1930 Hague Convention on Certain Questions Relating to the Conflict of Nationality Laws attempted to address these tensions by establishing rules for dual nationals, such as requiring third states to recognize exclusively the nationality of the state of habitual residence in cases of multiple nationality (Article 5), and affirming that states could treat dual nationals as their own domestically (Article 3).[14] However, the convention received only limited ratifications—fewer than 20 states—and failed to curb the incidence of multiple nationality or resolve inter-state disputes effectively, as it prioritized avoidance over elimination and lacked enforcement mechanisms.[8] The International Court of Justice's 1955 Nottebohm case (Liechtenstein v. Guatemala) further highlighted conflicts by requiring a "genuine link" or effective nationality for diplomatic protection claims, denying Liechtenstein's protection of naturalized Nottebohm against Guatemala due to his predominant ties to the latter, even absent formal dual status at the time.[74][75] Military obligations represent another domain of treaty-based conflict mitigation, where dual nationals may face simultaneous conscription demands from multiple states. The 1963 Council of Europe Convention on the Reduction of Cases of Multiple Nationality and on Military Obligations in Cases of Multiple Nationality sought to prevent such dual burdens by mandating loss of prior nationality upon voluntary acquisition of another (Article 1) and coordinating service to one state only, often based on residence or age at acquisition.[67] Yet, with limited adherence and subsequent policy shifts—such as the 1997 European Convention on Nationality, which permits states to allow multiple nationality without reduction requirements (Article 14)—these treaties have not universally resolved competing claims, leaving dual nationals vulnerable to enforcement by either state.[76] In bilateral investment treaties, conflicts arise when dual nationals attempt investor-state arbitration against a state of either nationality, with tribunals often denying jurisdiction under the "denial of benefits" clause or customary non-protection rules, though decisions remain inconsistent and debated.[77] Overall, while conventions like the 1961 UN Convention on the Reduction of Statelessness indirectly influence nationality practices by prioritizing avoidance of apatridy over multiple status, no comprehensive global treaty harmonizes obligations, perpetuating state sovereignty as the primary source of unresolved tensions.[78]Regional Variations in Policy
Europe and Supranational Entities
The acquisition and possession of multiple citizenships in Europe are primarily regulated at the national level, with the European Union (EU) deferring to member states' sovereignty over nationality laws under Article 9 of the Treaty on European Union. EU citizenship, which confers rights such as free movement and residence across member states, is automatically derived from holding the nationality of any EU member state and operates cumulatively alongside any additional nationalities permitted by the relevant state.[79][80] This framework accommodates dual or multiple citizenships without EU-level restrictions, though rare instances of dual EU-nationality (citizenship of two member states) trigger application of the "effective nationality" principle in diplomatic protection under the 1930 Hague Convention, prioritizing the state of habitual residence.[81] The Council of Europe, a supranational body encompassing nearly all European states, influences nationality policies through the European Convention on Nationality (ECN) of 1997, ratified by 21 members as of 2020. Unlike the earlier 1963 Convention on the Reduction of Cases of Multiple Nationality, which sought to minimize dual citizenship via renunciation requirements, the ECN explicitly permits multiple nationality in cases such as children acquiring citizenship from each parent of different nationalities, adoption, and state succession, while prohibiting arbitrary deprivation based solely on acquiring another citizenship.[16][82] The ECN also addresses military obligations for multiple nationals, requiring states to avoid double conscription through agreements, reflecting a shift from viewing multiple citizenship as a loyalty conflict to recognizing it as compatible with integration, albeit with persistent concerns over divided allegiances and electoral influences in host states.[16][83] European policies on multiple citizenship have liberalized since the 1990s, driven by migration needs, family reunification, and economic mobility, with 49% of global states now permitting it under varying conditions as of 2025; in Europe, this trend manifests in eased restrictions to prevent statelessness and enhance immigrant retention.[84][55] Germany, for example, enacted reforms on June 27, 2024, eliminating the prior requirement for most naturalization applicants to renounce their original citizenship, shortening residence periods to five years (or three for well-integrated individuals), and extending tolerances for children born abroad to German parents.[85] Similar unrestricted permissions exist in France, Italy, Portugal, Greece, Belgium, and Ireland, where naturalized adults and children via descent or marriage retain prior nationalities without compulsion to choose.[79][86]| Country | Dual Citizenship Policy for Naturalization (as of 2025) |
|---|---|
| Czechia | Permitted since 2014, no renunciation required.[56] |
| Denmark | Restrictions lifted; now generally allowed.[56] |
| France | Unrestricted for adults and children.[79] |
| Germany | Unrestricted since June 2024 reforms.[85] |
| Italy | Unrestricted, including via descent without generational limits.[79] |
| Netherlands | Restricted; renunciation generally required except for EU/EEA/Swiss citizens or refugees.[83] |
| Sweden | Eased restrictions; permitted for integration purposes.[84] |