Introduction
In the 2005 case of Roper v. Simmons,Footnote 1 the U.S. Supreme Court found that sentencing juveniles to death is a violation of the Eighth Amendment to the U.S. Constitution, which prohibits ‘cruel and unusual punishment’. The majority opinion, authored by Justice Anthony Kennedy, stated, among other things, that ‘Article 37 of the United Nations Convention on the Rights of the Child, which every country of the world has ratified, save for the United States and Somalia, contains an express prohibition on capital punishment for crimes committed by juveniles under 18’.Footnote 2 Adding this citation to the majority reasoning allowed J. Kennedy to offer his opinion on the executive and legislative branches’ treatment of international affairs, but Kennedy also appeared to reaffirm a seemingly growing trend in Supreme Court opinion writing: the citing of foreign or international law materials in domestic cases. Before Roper, the U.S. Supreme Court had again highlighted this practice by utilizing foreign or international law in several high-profile cases, including Lawrence v. Texas (2003)Footnote 3 and Grutter v. Bollinger (2003).Footnote 4
The participation of the U.S. Supreme Court in this transnational dialogue over the rights of children did not remain unnoticed by the Court’s specialized audiences, such as the legal academia, expert reporters and Congress,Footnote 5 but far less attention was paid to the number and diversity of legal briefs filed at the merits stage of the case, which cited various sources of foreign and international law. Simmons’ team of attorneys cited four international treaties and a decision by the Inter-American Court of Human Rights in their merits brief. Additionally, five amici, ranging from the American Civil Liberties Union to the European Union, included 37 citations to decisions by foreign national courts, international courts and multilateral treaties.
Despite some indication that lawyers and interest groups prompt U.S. courts to engage in transnational communication, the judicial globalization literature, at least in the United States, has mostly focused on the role that Supreme Court justices play in global judicial dialogue. In fact, expert scholars conceptualize judicial dialogue as a ‘horizontal process’ (Glensy Reference Glensy2011) that consists of ‘national government officials rather than international bureaucrats, decentralized and informal rather than organized and rigid’ (Slaughter Reference Slaughter and Byers2000). Research on the influence of litigants and other interested third parties on judicial behavior,Footnote 6 however, suggests that by ignoring actors such as lawyers and amici, we might be missing an important aspect of judicial globalization taking place in the face of even some of the most reluctant international participants.
In this study, we bridge the judicial globalization and American judicial behavior literatures to show that global judicial dialogue is a process driven (at least) in part by lawyers and interest groups that increasingly cite foreign and international legal materials, while acknowledging the well-established drive from above. We argue that adept amici and litigants provide American judges with valuable information regarding developments in foreign and international law and the latter’s relevance to the cases under adjudication. This, in turn, gives judges who are amenable to transnational communication the opportunity to validate international legal statutes and principles in their written opinions, which reasoning becomes valid legal guidance for future cases.
To test our argument, we follow a two-step approach. First, we employ an original dataset containing international law citations found in parties’ and amici briefs, as well as international law citations in U.S. Supreme Court opinions (majority and minority) from 1946 to the end of the 2023 term, to quantitatively uncover sequential associations in dialogue taking place among judges, litigants, and third parties. We then turn to a widely accepted international treaty that has not been ratified by the United States; the U.N. Convention on the Rights of the Child (from here on ‘CRC’ or ‘Convention’). The absence of ratification means that there is no domestic legislation that American judges can refer to; therefore, if used, judges would have to cite and engage with the international document and its provisions, which allows us to check whether judicial dialogue is taking place. After mapping parties’ and amicus curiae briefs, as well as CRC citations in all U.S. federal and state courts from 1987 to 2024, we turn our focus to three specific legal areas (juvenile sentencing, right to privacy, custody and family law) to map with specificity the evolution of argumentation and reliance on the Convention by litigants and judges. Some of the areas of analysis are legal areas where one would expect to see international legal principles and norms brought into the discussion or which judges rely upon, and some areas of analysis comprise what legal experts would classify as domestic law, either statutory or constitutional (Tushnet Reference Tushnet1999; Neuman Reference Neuman2004; Ramsey Reference Ramsey2004; Glensy Reference Glensy2011).
Our data indicate that (a) judges are much more likely to engage in transnational communication when provided with relevant arguments in merits or amicus curiae briefs, and (b) actors other than the judiciary are far more likely to initiate such communication, thereby playing an important role in the promotion of a global judicial structure, even when elected officials stall. Finally, this study lends support to earlier findings regarding the effect of legal briefs in the process of judicial decision-making and opinion-crafting.
Understanding who initiates and who participates in transnational legal dialogue is important because it speaks to the type, quality, and volume of information that judges receive from nonjudicial actors. Ultimately, the question of how transnational judicial dialogue takes place, who follows along, who adopts or rejects such arguments addresses the crucial issue of the outputs of courts, the latter which are far more likely to reflect international law preferences and interpretations of those who successfully gain access to the courts and employ such argumentation (Galanter Reference Galanter1974; Hazelton and Hinkle Reference Hazelton and Hinkle2022; Tippett et al. Reference Tippett, Alexander, Branting, Morawski, Balhana, Pfeifer and Bayer2022).
Judicial globalization from below
The steady increase in national courts’ reliance on foreign and international law citations in their opinions, labeled ‘transnational communication’, has established domestic judges as significant, independent actors in the international environment (Slaughter Reference Slaughter1994). As part of the process of judicial globalization, judges travel abroad, participate in international conferences, meet with colleagues in conferences and summer legal workshops and through this direct communication, they gather information about legal developments across borders (Slaughter Reference Slaughter2004).
Apart from this direct learning process, advancements in technology are also suggested to facilitate transnational communication among judges. Court opinions from various states are now translated into English and published online in specialized databases, making it easier for judges to consult foreign sources in the decision-making process where such sources would likely shed light on a legal problem (Slaughter Reference Slaughter2004; Collins Reference Collins2018). These developments, according to the literature, have promulgated domestic judges into significant actors in the establishment and enforcement of international law domestically, especially when it comes to the effective enforcement of international human rights (Diel, Ku, and Zamora Reference Diel, Ku and Zamora2003: 50; Sandholtz Reference Sandholtz2015; Simmons Reference Simmons2009; Waters Reference Waters2007: 633).
Considering the literature’s focus on the judge as an individual with cosmopolitan preferences (Breyer Reference Breyer2015), it is not surprising that the few studies that move beyond a normative discussion of the phenomenon in the U.S. context choose to pay attention to the ways judges utilize transnational sources. Even in this aspect, studies have produced mixed conclusions, since on one hand, Supreme Court justices appear to engage in this behavior strategically, to increase the persuasiveness of their reasoning (Black et al. Reference Black, Owens, Walters and Brookhart2014), and, on the other, federal judges are suggested to make an extremely limited use of transjudicial communication, mostly in cases that already involve some aspect of foreign law (O’Brien Reference O’Brien2006; Zaring Reference Zaring2006).
We argue that to better understand the process of judicial globalization, we should move our focus beyond judges as the sole force in the embrace and routinization of international norms in the domestic sphere and examine other actors with a potentially equally important impact on the proliferation of transnational communication. As research on the rights revolution has shown, willing judges are not the only necessary condition for the development of domestic law; strategic advocacy pressuring the judiciary from below is also required (Epp Reference Epp1998).
This emphasis on pressures from below is also present in the international environment, where international organizations and transnational activist networks attempt to convince states to adopt and enforce international norms domestically. In such instances, international organizations function as teachers of international norms (Finnemore Reference Finnemore1993, Reference Finnemore1996), and transnational and activist networks push for their internalization on the ground (Keck and Sikkink Reference Keck and Sikkink1998; Risse-Kappen, Ropp, and Sikkink Reference Risse-Kappen, Ropp and Sikkink1999). This ‘transnational civil society’, in many ways similar to the one in the United States during the years following Brown v. Board of Education Topeka, KS,Footnote 7 is suggested to have helped judges around the world acquire the status of independent actors in the international system (Kersch Reference Kersch2005).
Similarly, judges acquire information from the briefs submitted by litigant parties. Litigant briefs on the merits familiarize judges with the facts of a case and inform them about the legal authorities pertinent to the issue. Judges, in turn, when they construct written opinions, give special attention to the language used in the merits briefs, since they appear to rely on them more, compared to language stemming from lower court opinions and amicus briefs (Feldman Reference Feldman2017; Hazelton, Hinkle, and Spriggs Reference Hazelton, Hinkle and Spriggs2017). In fact, certain Supreme Court justices seem to use merits briefs as their main tool in the process of opinion writing, by lifting extensive parts of the opinion language directly from the parties’ briefs (Feldman Reference Feldman2016; Corley and Feldman Reference Corley Pamela and Feldman2023). This evidence informs us that ‘the parties, through the briefs submitted on the merits, can influence the content of opinions, and consequently, have the ability to influence the law’ (Phillips Reference Phillips1998; Corley Reference Corley2008). Put in different terms, studies on litigant language and influences on judicial opinion-writing speak to the variety and universe of arguments judges are likely to be exposed to and subsequently obliged to respond to, thus setting the agenda for the dialogue that will ensue between judicial and nonjudicial actors, and controlling the outcome of such exchanges (Manz Reference Manz2002).
An additional method used by groups and litigants to promote the internalization of foreign and international law by the domestic judiciary is by filing amicus curiae briefs that cite foreign and international law, since such briefs allow parties to communicate to judges what they think the interpretation of a law should be (Collins, Corley, and Hamner Reference Collins, Corley and Hamner2015). Judges, on the other hand, trying to gather as much reliable information as possible regarding the case under deliberation, commonly find amicus curiae briefs useful due to the expert status of interested third parties (Epstein Reference Epstein1993; Collins Reference Collins2008).
Specifically, amici briefs can include reliable information regarding the wider consequences of a case outcome (Caldeira and Wright Reference Caldeira and Wright1988; Collins Reference Collins2004), as well as arguments and authorities missing from the parties’ briefs (McGuire Reference McGuire1993; Kearney and Merrill Reference Kearney and Merrill2000). These particular characteristics of amicus briefs make them an effective tool of influence on U.S. Supreme Court justices, for example, who often adopt the language and authorities included therein (Collins, Corley, and Hamner Reference Collins, Corley and Hamner2015; Ennis Reference Ennis1984; Epstein and Kobylka Reference Epstein and Kobylka1992; Owens and Epstein Reference Owens and Epstein2005; but see Spriggs and Wahlbeck Reference Spriggs and Wahlbeck1997).
If the content of an opinion produced by the Supreme Court is shaped to such a great extent by the parties involved in litigation (Phillips Reference Phillips1998), and by ‘friends of the court’ with an interest in the outcome of the case (Wahlbeck Reference Wahlbeck1997; Collins, Corley, and Hamner Reference Collins, Corley and Hamner2015; Hazelton, Hinkle, and Spriggs Reference Hazelton, Hinkle and Spriggs2017), then, the instances of transnational communication occurring through court opinions might not be solely a result of a judge’s active search for these authorities, but the result of being prompted with this type of language in the briefs. As such, we argue that, just as social science sources made their way into Supreme Court opinions through briefs (Margolis Reference Margolis2000; Epstein and Black Reference Epstein and Black2007), the inclusion of foreign and international law authorities in litigant and amici briefs informs judges of legal developments beyond domestic borders, along with their potential applications on a case.
In light of the above considerations, we put forth the following propositions:
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a) Reliance on transnational authorities in the merits or amicus curiae briefs of a case increases the likelihood of transnational legal dialogue on the part of judges.
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b) Nonjudicial actors, being the first to cite cosmopolitan legal sources in the litigation process, will more frequently use such material than will judges.
It should be noted at this point that we do not theorize on the reasons behind a judge’s choice to engage in transnational communication. Judges who rely on foreign and international law in their written opinions might do so because they consider these authorities persuasive, or because they have adopted a cosmopolitan attitude, or because it aligns with personal policy-making goals. Regardless of the motivation, the fact is that transnational citations do appear and form part of court opinions; the focus of this study then must be the route that these citations follow to become part of a court’s language, to elucidate the role of nonjudicial actors in bringing international law home.
The next two sections test these propositions through two distinct approaches. In Part III, we quantitatively analyze the influence of litigant and amicus curiae briefs that contain argumentation relying on any international legal doctrine, norm, treaty or agreement within all U.S. Supreme Court majority and minority opinions from 1946 to 2024. In Part IV, we turn our attention to a nonratified by the United States international treaty, the U.N. Convention on the Rights of the Child, and qualitatively assess our propositions through a language and sequence-focused analysis of Convention-based argumentation in U. S. courts, as well as through tracing the character and scope of nonjudicial actors that have been engaging in this dialogue. This twofold approach aims to (a) uncover broad judicial and nonjudicial actors’ behavioral patterns concerning the use of international legal materials, and (b) elucidate the iterative process of transnational legal dialogue.
The role of nonjudicial actors in transnational legal communication
For this study, transnational communication refers to the citation of international treaties, customary international law and decisions reached by international courts.Footnote 8 Our analysis focuses on the U.S. Supreme Court and its citation practices from 1946 to 2024. This time range covers the proliferation of international agreements following the end of World War II and simultaneously ensures the availability of comprehensive data for the purpose of analysis of litigant and amicus briefs at the merits stage.
To test our propositions, we created an original dataset of international law citations in Court opinions, litigants and amici briefs. To construct this initial dataset, we identified the universe of briefs that mention international law, specific treaties such as the International Covenant on Civil and Political Rights and the Convention Against Torture or decisions by international courts, such as the International Criminal Court. We identified 413 Supreme Court cases with citations to international legal sources in litigants’ briefs and 383 cases with international legal references in amicus curiae briefs. From those, 185 cases featured citations in both litigant and amicus briefs.
Next, we classified Supreme Court opinions based on whether they engaged in transnational communication or not. Following the same coding procedure, we identified 189 cases that referred to transnational authorities, of a total of 9277 cases. From these, 146 included at least one citation in the majority opinion. Table 1 provides a descriptive look into citation patterns by justices, litigants and amicus briefs. The majority of court opinions in the timeframe do not include citations of international legal authorities of any kind. From those 189 cases that do cite international law, in 56 cases, the justices do so without being prompted by lower parties. However, the number of citations by litigants and amici that later prompt discussion by the justices is double the number of sua sponte occurring discussions. Moreover, litigant briefs appear to enjoy slightly higher rates of adoption into Court opinions compared to amicus briefs (1.3% vs. 1.1% of opinions).
Table 1. Frequency of international law citations in court opinions, litigant briefs, and amicus briefs
To test whether international law reliance in the merits and amicus briefs increases the likelihood of judges engaging in transnational legal dialogue, and whether nonjudicial actors in general are more likely to initiate this dialogue, we combined our international law citations dataset with Spaeth Supreme Court Database variables. Our dependent variable, Opinion Citation, was coded 1 for cases that include at least one citation to an international legal authority anywhere in the majority or minority opinion(s) and 0 otherwise. Our secondary dependent variables, Majority Citation, Concurrence Citation and Dissent Citation were coded 1 for opinions that include at least one citation to an international legal authority, and 0 otherwise.
Our two main independent variables, Party Brief Citation and Amicus Brief Citation, were coded 1 if a reference to transnational law occurred in one of the litigants’ or in at least one of the amici briefs. On the contrary, if the briefs cited only domestic law, these variables were coded 0. Additionally, to account for how effective litigants and amici are in prompting judges to engage in transnational communication based on repetition and intensity of signals, as some studies on briefs suggest (Collins, Corley, and Hamner Reference Collins, Corley and Hamner2014; Fitzgerald Reference Fitzgerald2019), we record the number of amicus briefs filed in a case that cite international legal materials. As such, our Number of Amici variable measures the number of separate briefs citing international law in a single case.
The study’s main inquiry into the route of transnational legal dialogue brings forth essential secondary arguments on the behavior of legal actors and institutional effects that may promulgate the communication patterns we attempt to explain. In the models below, we control for other factors that might affect the language and sources Supreme Court justices use in their opinions. First, we control for the effect that a case involving a foreign relations issue might have on the likelihood of citing international legal material in both judicial opinions and all types of briefs (Zaring Reference Zaring2006). A case that requires the justices to engage in treaty interpretation, for instance, is almost certain to attract transnational citations in the resulting opinions because the former have to discuss and apply the treaty, but also in the briefs, as parties offer their own interpretation of authorities. To construct the variable Foreign Issue, we employed data from the Supreme Court Database (Spaeth et al. Reference Spaeth, Epstein, Nelson and Martin2024) and coded cases for which the petitioner or respondent related to a foreign issue or entity as 1, and 0 otherwise.Footnote 9
Furthermore, to control for the effect of a case’s importance on the likelihood of citation (Black et al. Reference Black, Owens, Walters and Brookhart2014), including earlier explanations of transnational communication, we incorporate two variables from the Supreme Court Database, namely, Overturn Precedent and Judicial Review, in our models. Cosmopolitan Justice captures whether the majority opinion author expressed openness toward international law in interviews, confirmation hearings, by studying international law abroad or by lecturing/teaching/visiting colleagues and law schools abroad (Slaughter Reference Slaughter2004; Black et al. Reference Black, Owens, Walters and Brookhart2014; Fitzgerald Reference Fitzgerald2019). Opinion Direction assesses the likelihood of citing international legal authorities in a case’s resulting opinions, depending on the ideological direction of each opinion, which is coded 1 for a conservative and 2 for a liberal opinion direction. Finally, the models include a Supreme Court Term variable to check for the proliferation of transnational judicial communication in the late 1990s (Slaughter Reference Slaughter2004), and a Constitutional Interpretation variable that records any effects on transnational legal citations based on the legal issue area involving statutory or constitutional interpretation (Bailey and Maltzman Reference Bailey and Maltzman2011).
Figure 1 presents results for all four logit models, which assess the effect of the use of international law on behalf of litigants and friends of the court, respectively, on the content of the Court’s overall case output, majority opinion, concurrences and dissents. Our main independent variables, Party Brief Citation and Amicus Brief Citation, are statistically significant and moving in the expected positive direction in all four models. U. S. Supreme Court justices are more likely to include transnational citations when litigants and amici provide them with information about international law. Furthermore, these results hold true when controlling for other factors, such as specific characteristics of a case or judicial attitudes. Likewise, as the number of amicus briefs that cite international law authorities increases, so does the likelihood of a justice’s participation in such dialogue in a majority or concurring opinion; a finding that matches prior studies on the cumulative influence of amici.
Figure 1. Logistic regression on the effect of litigant and amici citations on opinion content.
Addressing a logical point on the use of international law argumentation, our results indicate the statistical significance of the presence of a foreign issue/entity in a case on the likelihood of parties prompting justices with such arguments. We observe a difference in the likelihood of this phenomenon occurring depending on the type of judicial opinion issued, with international law citations positively influencing pertinent judicial discussion in the majority and dissenting opinions (p<.05). Calculating the same likelihood for the presence of citations anywhere in the Court’s opinion is positively significant at the p<.01 level. On the other hand, we cannot confirm prior research expectations regarding the effect of briefs with international law citations on ‘important’ cases, that is, when justices engage in judicial review or overturn established precedent (Black et al. Reference Black, Owens, Walters and Brookhart2014), as the two variables do not reach statistical significance in any of the models.
Similarly, we do not find evidence that justices with cosmopolitan attitudes are more likely to cite international law when they author the Court’s opinion, or that international law is used to support judicial outcomes with liberal ideological tendencies (ibid., 23). However, we do find a limited connection between dissenting opinions that support a liberal policy outcome, and the likelihood that their author uses international law to support that outcome; Dissent Decision Direction is statistically significant at the .01 level in the Dissents Model. Lastly, our Term and Constitutional Interpretation variables similarly do not remain consistently significant across all models.
To better understand the magnitude of the effect that international law citations in parties’ briefs have on judicial transnational communication, we perform a predicted probabilities test for our two independent variables in all four models (see Figure 2 below). With the remaining variables set to their mean, an international law citation significantly increases the probability that the Court cites such material. Specifically, when looking at the predicted probability of an international law citation present anywhere in the Court opinion, when lower party briefs cite only domestic sources, the probability that the Court cites international law material is 0.7%. This probability increases to 2% and 9% when amici or litigant parties respectively cite international law. Remarkably, when both litigants and amici present argumentation based on international authorities, the probability increases to 26%.Footnote 10
Figure 2. Predicted probabilities of international law citation in opinion content.
Addressing our propositions above, the results lend support to both. First, international law citations in litigant and amicus briefs correlate with an increased likelihood that a Court opinion will cite a similar source. Results hold across all models when controlling for other potential influences on the Court’s citation practices and strongly confirm our proposition that reliance on transnational authorities in the merits or amicus briefs of a case increases the likelihood of transnational legal dialogue on the part of judges.
Second, during the period studied, litigants and amici employed international legal argumentation far more frequently than justices did; 611 cases in our sample included such citations on behalf of either litigants or at least one amicus. Yet the Court only referred to international law in 189 cases, 133 of which were instances of justices responding to an already posed argument by lower parties. We can, therefore, confirm with confidence our second proposition that – compared to justices – nonjudicial actors are far more likely to initiate transnational judicial dialogue in the litigation process, at an odds ratio of 3:1, that is, for every sua sponte international law citation by a Supreme Court justice, there are three such instances raised by litigants or amici.
A framework of analysis for ushering the convention into domestic dialogue
After uncovering broad behavioral patterns, we test our propositions on nonjudicial actors and transnational dialogue through the tracking of CRC citations and references in published court opinions. Using Westlaw, we conducted archival searches to identify court opinions, litigant briefs on the merits and amicus curiae briefs relying on the CRC, which yielded a dataset of 119 federal court opinions, 32 state court opinions, 50 litigant briefs and 99 amici briefs.Footnote 11 We then classified the citations based on eight broad legal areas and denoted the disposition that the party/judge took vis-à-vis the Convention as a type of argument (positive/negative/neutral).
The transnational judicial dialogue literature focuses on judges and courts as agents promoting mechanisms of coordination that exercise judicial review of rights through transnational dialogue (Sandholtz Reference Sandholtz2020). We, therefore, operationalize the Roper v. Simmons opinionFootnote 12 as the pivotal moment for the Convention in this particular global exchange, because through it, the highest court of the land signaled to its various audiences the CRC’s valid status as a tool of persuasion and an authority to pay attention to. Our propositions instead place lower parties at the forefront of this practice, which, to some extent, may seem contrary to literature expectations. Nevertheless, because prior studies would place Roper as the definitive point in dialogue development and judges as the initiators of this process, we follow the literature’s approach to investigate the role judicial and nonjudicial actors played pre- and post-Roper and assess our propositions.
The first-ever CRC citations in U.S. courts occurred in the amici briefs submitted by Amnesty International, International Human Rights Law Group and Defense for Children International in 1987, in a Supreme Court case dealing with the death penalty of a juvenile under 16 years of age, three years before the Convention became effective.Footnote 13 While the U.S. Supreme Court did not cite the principles arising from the Convention’s preparatory work, the plurality opinion authored by Justice Stevens took into consideration the views of other nations to declare the imposition of the death penalty on juveniles under 16 years of age a violation of the Eighth Amendment to the U.S. Constitution, explicitly citing the information submitted by Amnesty International.Footnote 14 The concurrence to the Court’s decision by Justice O’Connor also made a passing nod to an ‘international agreement, signed but not ratified by the United States’;Footnote 15 a reference to the Convention’s status of ‘signed but not ratified’.
As seen in Figure 3, in the years following the first CRC mentions until March 1, 2005, and Roper, we encounter additional citations in 19 amicus and five litigant briefs filed at the U.S. Supreme Court, in eight U.S. Courts of Appeals and eight U.S. District Courts opinions and in at least seven litigant briefs at the U.S. District and Appeals levels.Footnote 16 During the same time, we observe 10 CRC citations in state court decisions and at least five citations by state litigants. These cases cover issues ranging from the deportation of minors to family law, the Alien Tort Claims Act and the juvenile death penalty. While obtaining the complete universe of state litigant briefs specifically is not possible due to the lack of such an inclusive jurisdiction legal database, we find the existing evidence suggestive of the trend and direction of citations in state courts, as well as probative of the importance of state nonjudicial actors in transnational legal dialogue. During this phase, when the treaty had not been ratified but groups were still optimistic about the U.S. joining, we can observe nonjudicial actors engaging in the ‘information’ function, where they supply judges with ‘appropriate’ methods for applying foreign rules in domestic cases (Zaring Reference Zaring2006; Collins Reference Collins2008).
Figure 3. Number of Convention citations by type per year.
Looking at total numbers for the pre-Roper era, litigants and amici positively argued on behalf of the Convention, that is, urged the courts to adopt a legal outcome based on the principles and articles of the nonratified treaty, 40 times. Judicial actors, during the same period, formally discussed or referred to the Convention 26 times; however, these references were mixed in purpose, with some being positive, some negative (i.e., the Convention is a nonbinding or inappropriate authority) and some neutral.
While the U.S. Supreme Court formally cited other international legal sources in decisions it renderedFootnote 17 in the period preceding 2005, it did not cite the Convention until Justice Kennedy in Roper added the treaty to a growing list of international authorities the Court has used. Here, the respondent and several amici had asked the Court to include the Convention in its consideration of the case, while the petitioner and other amici objected to the incorporation of international law in a case concerning domestic constitutional law.
Since Roper, CRC citations by amici at the Supreme Court have been steadily increasing; the authority has been put forth in cases ranging from marriage equality to abortion restrictions, and by friends of the court ranging from the National Association of Evangelicals to Human Rights First, or international law scholars. The expansion of the network of citations has also occurred at the lower federal and state court levels. Between the Roper decision and the end of 2024, litigants and amici cited the CRC in 121 documents at the U.S. Supreme Court level (45 merit and 76 amici), 26 times in U.S. Circuit Courts of Appeal, 47 in U.S. District Courts and a minimum of 15 in state courts, for a total of 209 citations. During the same timeframe, federal circuit and district court judges referred to the Convention 101 times (40 circuit and 61 district) and state judges 22 times, for a total of 123 citations – almost half the number of citations filed by nonjudicial actors.
A major post-Roper moment for the Convention arrived in 2010, when the Supreme Court found that life imprisonment without parole for juveniles constituted a violation of the Eighth Amendment’s prohibition on cruel or unusual punishment.Footnote 18 In his opinion, Justice Kennedy mentioned that both the petitioner and several of the amici, including the American Bar Association, the Center for Law and Justice and the American Association of Jewish Lawyers, referred to the respective CRC provision to support their arguments. To interpret the Constitution’s clause of ‘cruel and unusual punishment’, Justice Kennedy employed the ‘polling other jurisdictions’ method to examine how the international community defines acceptable and proportional punishments for juveniles. For the various audiences of the Court paying attention to doctrinal evolution, the citation marked the Court’s second signal that the Convention was a tool of persuasion to consider, especially when the language of the law at hand is unclear and the issue serious.Footnote 19
Overall, from 1987 until the end of 2024, the Convention has been cited in two Supreme Court decisions; in both of these cases, the treaty was discussed on the merits and multiple amici briefs. Covering the same span of years, the Convention’s provisions have been cited in 99 amici and 50 merits briefs and petitions for a writ of certiorari. At the federal courts of appeals, whose decisions make up the bulk of precedent in the American scheme of justice, 60% of court opinions referring to the Convention state that the issue had been raised by one of the litigants (29 of 48 cases). This rate reaches 74% (51 of 69 cases) and 63% (20 of 32 cases) for federal district courts and state courts, respectively; in other words, an overwhelming portion of transnational dialogue on the CRC was initiated by nonjudicial actors (see Table 2).
Table 2. Number of CRC court citations and treatment
Based on our mapping, we revisit the propositions and conclude that in the case of this special, universally accepted treaty, but for the United States, nonjudicial actors were not only as important in disseminating persuasive CRC principles, but even more active than judicial ones. This finding remains robust for the period before and after the Court’s Roper signal. With regard to our first proposition, textual analysis of court opinions validates our expectation that reliance on transnational authorities in the merits or amicus curiae briefs of a case is associated with an increased likelihood of transnational legal dialogue on the part of judges. In fact, a sizeable majority of court opinions referenced CRC arguments – first posed in litigant and amici briefs – by repeating arguments and passages verbatim, as research on the influence of briefs has shown (Collins, Corley, and Hamner Reference Collins, Corley and Hamner2015; Corley Pamela and Feldman Reference Corley Pamela and Feldman2023).
The importance of judicial actors in this dialogue is not to be minimized, as can be observed from the proliferation of CRC argumentation after the Court’s signal in 2005. Our argument rather focuses on the role of nonjudicial actors. In the following section, we look at selected legal areas and analyze how CRC argumentation has been used by judicial and nonjudicial actors alike. We also attempt to uncover any patterns in the dialogue, for example, in concerted efforts by litigants, as well as delve into the evolution of how the Convention’s doctrine has been understood. The three legal areas below (juvenile sentencing, child custody, right to privacy) present three different dialogue patterns taking place among actors-participants. Table 3 presents all patterns uncovered based on the universe of cases and briefs coded.
Table 3. Patterns of dialogue participants per issue area
Dialogue-mapping distinct legal areas
i. Juvenile sentencing
The Roper analysis is revealing of the high rate of CRC argumentation taking place in the area of juvenile sentencing. The language of the Convention’s text being clearly prohibitive of execution or life without parole sentences for children under 18, the amicus briefs filed in Roper by Amnesty International, International Human Rights Law Group (IHRLG) and Defense for Children International instead jointly focused on the reservations placed on the record by the U.S. representative to the Working Group during the preparatory stage of the Convention. However, according to IHRLG, the reservation against the prohibition of the death penalty to minors was not formally placed by the U.S. representative on behalf of the government, and only stipulated that the Working Group would later return to that point, which event never took place.Footnote 20
The customary status of forbidding excessive punishment for juveniles, along with whether the Convention was self-executing in the United States, remained the focus of the debate, with the United States citing the Convention in an amicus brief in support of the state of Nevada so as to remind the Supreme Court that Congress had not ratified the treaty.Footnote 21 During the same time, several state and lower federal court judges dismissed litigant arguments based on the Convention due to its non-self-executing nature.Footnote 22
Amici and litigants, on the other hand, pointed to the near-universal ratification of the Convention. The argument that all nations, except the United States and Somalia, had ratified and adhered to the CRC appears in numerous briefs supporting a ban on excessive sentencing of juveniles.Footnote 23 Advocates for the incorporation of the Convention saw the moment was ripe for acknowledging this customary norm, or at least acknowledging its ‘steady progress toward a peremptory norm’,Footnote 24 based on its acquiring a remarkable number of signatory states by 2005. Amici equally argued that the number of signatory states had turned CRC provisions into customary law, and that, while states have the ability to place reservations in treaties according to Article 2.1(d) of the 1969 Vienna Convention on the Law of Treaties, they cannot do so if the reservation is diametrically opposed to the Convention itself.
The worldwide growing opposition to excessive punishment for juveniles was picked up and noted by several judges,Footnote 25 with some of them even applauding the practice. Judge Spina for the Supreme Judicial Court of Massachusetts, Suffolk, noted, ‘as John Adams recognized over 215 years ago, we belong to an international community that tinkers toward a more perfect government by learning from the successes and failures of our own structures and those of other nations’.Footnote 26
On the other hand, the formal position of the government remained steadfast that the United States objected to the proposed ban on juvenile executions and that the Senate had not ratified the Convention. It was joined by ideologically conservative amici, such as the Solidarity Center for Law and Justice, members of the U.S. House of Representatives and some statesFootnote 27 arguing that incorporation of the unratified Convention would be undemocratic and that the provisions of Article 37 had not reached customary law status.
The second main argument promoted by amici and litigants was that even if the United States had not ratified the Convention, the latter had been signed. A brief filed by President Carter and others in a series of Supreme Court cases suggested that ‘according to Article 18(a) of the Vienna Convention on the Law of Treaties, signatories to treaties must not act in a manner that defeats the object and purpose of the treaty. By continuing to sentence child offenders to death, the United States is failing to abide by the Convention on the Rights of the Child in good faith as promised’.Footnote 28 The same position was promoted in an amicus brief by the European Union.Footnote 29
Eventually, the above pro-Convention arguments were adopted by the U.S. Supreme Court in Roper v. Simmons (2005). Finding the imposition of the death penalty upon juveniles under 18 unconstitutional, Justice Kennedy stated that ‘it is fair to say that the United States now stands alone in a world that has turned its face against the juvenile death penalty’,Footnote 30 however, not without raising strong objections from dissenting justices. Five years later, Justice Kennedy, writing for the majority, followed the same approach to strike down laws imposing life sentences without parole for nonhomicide offenses in Graham v. Florida (2010).Footnote 31
The evolution of the CRC’s use in juvenile sentencing directly speaks to our two propositions. First, it demonstrates how courts adopt litigant and amici arguments into the language of their opinions and subsequently, the influence nonjudicial actors can exert upon formal dialogue. Second, juvenile sentencing presents an area where litigants and amici actively debated on the meaning of the Convention’s text at a higher rate compared to judicial officers, and before there was an indication of it being an acceptable practice. In this instance, of course, litigants and amici found willing dialogue participants in the courts.
ii. Child custody
During the course of the 20th century, global interest in family law propelled a ‘worldwide trend…which is to view the child as a subject of law with his or her own rights – including the right, even for a very young child, not to be made into a football which is the property of the latest person to grab and run with it’, as a litigant described in their certiorari petition to the U.S. Supreme Court.Footnote 32 The area also poses an interesting finding for the focus of this study on CRC’s reach into American legal argumentation, because the first arguments relying on it were made in state courts by litigants well before Justice Kennedy signaled to audiences in Roper that the Convention was appropriate argumentation to raise in cases involving the rights of children and minors.
Under the literature’s conceptualization of judicial dialogue, our CRC key event is the 2005 Roper opinion because, in its text, the Court converses with international agencies, state representatives and bureaucrats, as well as foreign courts and their judges, in a manner that introduces the Convention to American judges and litigants. Following the same pre- and post-Roper pattern in family and custody law cases, it was litigants in state and tribal courts that first proposed relevant arguments as early as 1992. Of five state and tribal court cases discussing the Convention before 2005, we make two noteworthy observations; first, all five mentions by the authoring judges and justices have a positive disposition toward the Convention. In one case, Judge Dranginis of the Superior Court of Connecticut even shared his thoughts regarding the U.S. government not acting to ratify the Convention:
Of significance to this court is Article 12 of the United Nations Convention on the Rights of the Child adopted by the General Assembly of the United Nations on November 20, 1989. It is of great concern and embarrassment that the United States of America is not a signatory to that convention.Footnote 33
The second observation of note is that two of the pre-Roper mentions were featured in opinions by the Supreme Judicial Court of Massachusetts and the Supreme Court of the Navajo Nation. Both opinions responded to relevant litigant arguments and acknowledged that the Convention had not been ratified by the United States; nevertheless engaged with the relevant articles, and found that the lower courts in their respective systems had acted ‘completely in accord with principles expressed therein (Convention articles)’.Footnote 34
Returning to our propositions, post-2005, we observe a similar pattern of growing Convention discussion in state court opinions, prompted by litigants, as well as the Convention being reviewed in federal court opinions, petitions for certiorari to the U.S. Supreme Court (but no case in that legal area ‘making it’ to the Court) and amicus briefs. Judges’ disposition toward the Convention’s status as appropriate doctrine is more varied in this area, with the Alabama Supreme Court, for example, showing signs of rejection,Footnote 35 neutral references during mostly disposal proceedings, but also positive treatment, especially by the U.S. Court of Appeals for the Fifth Circuit. There, Judge ClementFootnote 36 referred to the Convention’s principle of ‘treating a child as an individual and protecting his or her identity as an individual’ being a ‘concern that also lies at the core of the liberty guaranteed in the Fourteenth Amendment’.Footnote 37
The number of cases in family and custody law that rely on or discuss the Convention does not allow us to draw any connections between litigants to identify concerted efforts to make its provisions binding. However, we do know that all formal discussion in custody court opinions was initiated by the litigants, except for the Fifth Circuit’s Abbott case above. We find the evidence gathered from existing data suggestive of the rate and trend of CRC argumentation to be initiated by litigants, instead of judges.
In federal court, no linkage among special interests could be identified from the amici either. After 2005, we observed the first amicus briefs featuring claims that the Convention supported their position in custody and international child abduction cases. While all parties submitting briefs in these cases were nongovernmental organizations and legal/academic centers, the arguments vary in terms of their goals. These amici seem to mainly focus on Article 3 of the Convention,Footnote 38 emphasizing that the courts’ priority should lie with the best interests of the child. Nevertheless, the amici have divergent views on what ‘best interests’ translates to, with the battle revolving around the legal impact that focusing on the ‘rights of the child’ vs. focusing on the ‘rights of parents’ would have.
For instance, the advocacy group Them Before US argues it takes the approach of children’s interests first; however, the group interprets those interests to lie exclusively with securing the presence of a father and a mother in the child’s life.Footnote 39 Other amici also advocate in favor of the relevance of the protections that the Convention bestows on the U.S. scheme of justice, but instead, take a more textually faithful approach to Article 3. The London-based charity organization Reunite International Child Abduction Centre advised the Supreme Court, for example, that it cannot apply the provisions of the 1980 Hague Convention on the Civil Aspects of International Child Abduction – the United States being a signatory party – without considering the CRC, whose goals align with the former’s in ensuring that ‘the best interests of the child’ approach is taken by courts on a case-by-case basis, rather than categorically.Footnote 40 Similar to what we observed in other legal areas, the Convention is already being brought into the global judicial dialogue to be used as a tool of persuasion that serves divergent policy results.
In terms of our propositions, dialogue in this legal area flows from litigants/amici to the courts in a bottom-up process, lending support to the important participant status of nonjudicial actors in the expansion of international legal principles. Additionally, the parties’ active involvement in this dialogue produces legal material that can be referenced, cited and relied upon by courts, even though well-defined legal outcomes have not been reached by courts.
iii. Right to privacy
A legal area in which arguments have been marked by increasing CRC reliance in recent years is the right to privacy; a right not explicitly stated in the U.S. Constitution, rather one that has been found to emanate from the substance of various liberties textually located in the First, Third, Fourth, Fifth, Ninth and Fourteenth Amendments to the U.S. Constitution.Footnote 41 While American courts have not cited the Convention in right-to-privacy cases, amici have applied its logic in marriage equality and access-to-abortion cases, because protection of and against encroachment of these liberties was subsequently interpreted to emanate from the right to privacy.Footnote 42 In other words, until 2022, the right to privacy was interpreted to encompass the right to sexual liberty, to marry the person of one’s choice and to reproductive choice, among others.Footnote 43 Interestingly, the majority of transnational citations in juvenile sentencing cases were in support of the rights of criminal defendants. In privacy cases, on the other hand, the Convention has often been cited by groups advocating for a restrictive interpretation of the right, so as not to expand its coverage to same-sex marriage, and restrict abortion access.
In Amnesty International’s brief in Lawrence v. Texas (2003), the Convention was used to support the right to privacy as extending to sexual liberty, because it contains a sexual orientation equality provision. Starting with Hollingsworth v. Perry (2013), U.S. v. Windsor (2013) and Herbert v. Kitchen (2014), however, the focus by amici moved to Article 7(1) of the Convention, stating that ‘as far as possible, a child has the right to know and be cared for by his or her parents’. Groups, such as the Ethics and Religious Liberty Commission of the Southern Baptist Convention, Catholics for the Common Good and the National Association of Evangelicals, interpreted the treaty provision to be supportive of ‘traditional’ marriages that are ‘fully recognized in international human rights law’.Footnote 44 According to these amici, ‘marriage as a social institution has served the purpose of maximizing the chances that children will be reared by their biological mother and father in a committed bond; a purpose recognized as a moral right by the United Nations Convention on the Rights of the Child’.Footnote 45 This take on article 7(1) of the Convention, which switched the word ‘parents’ to the words ‘biological mother and father’, continued to be advocated in same-sex marriage cases until Obergefell v. Hodges (2015), where Justice Kennedy, once again authoring the Court’s majority opinion, declared all state laws banning same-sex marriage unconstitutional. Unlike prior decisions interpreting the right to privacy as it applies to sexual liberty and marriage equality, Justice Kennedy’s opinion in Obergefell did not consider transnational legal principles or doctrine.
Despite failing to persuade the Court to accept the restrictive interpretation of the CRC, some interest groups have continued its use in privacy cases, specifically those advocating for the criminalization of abortion in the United States. Here, these amici have focused on the Preamble of the Convention stating that a child ‘needs special safeguards and care, including appropriate legal protection, before as well as after birth’.Footnote 46 Three amici, namely 141 International Legal Scholars, the Center for Family and Human Rights and the European Center of Law and Justice, used the same provision to support the overturning of Roe v. Wade (1973) in Dobbs v. Jackson Women’s Health Organization (2022), while also emphasizing its near universal ratification.Footnote 47
The right to privacy, overall, as Justice Brandeis put it, encompasses ‘the right to be let alone’ from government intrusion into individuals’ private lives.Footnote 48 NGOs, in response to the arguments above, pressed upon the Court’s own precedent, which they linked to a different interpretation of the Convention’s preamble based on Committee General Comment No. 20 (2016), according to which ‘human rights treaty obligations encompass the reproductive rights of women and girls’.Footnote 49 These groups noted that, while the CRC’s preamble refers to ‘legal protection before as well as after birth’, ‘this was never intended to trump women and girls’ right to life in the context of abortion access’.Footnote 50 Nevertheless, Justice Alito, writing for the Court’s majority, sided with Dobbs and discussed abortion policies outside the United States without making any specific references to the Convention or amici arguments, determining that the right to privacy did not include a right to abortion anymore.
The recent retirement of Justices Kennedy and Breyer, and the passing of Justice Ginsburg, key supporters of the Court’s transnational take on rights, could signal the death knell for judicial globalization via the U.S. Supreme Court (Bob Reference Bob2012: 76). Yet the espousal of the Convention by conservative amici shows a new, perhaps not so unexpected, turn; one somewhat more palatable to the Court’s current conservative majority. Since Lawrence and Roper, legal scholars have pointed to the unpredictability in terms of litigants’ desired outcomes when using international or foreign legal doctrine, due to the latter’s capacity to be used for arguments that could support both rights-restrictive and rights-expansive goals. As Calabrese and Zimdahl put it (Reference Calabresi and Zimdahl2005: 751), ‘foreign law is more conservative than U.S. constitutional law with respect to separation of church and state, admission of illegally obtained evidence and allowance of governmental restrictions on speech’. While nonjudicial actors seem fully engrossed in a transnational dialogue on the CRC’s applicability to right-to-privacy cases, as seen by recent briefs filed in abortion-restrictions cases post-Dobbs,Footnote 51 judges have not yet engaged. Nevertheless, the Convention and its meaning remain matters of discussion in U.S. courts because of litigant efforts, with outcomes to be determined.
Conclusion
This study aimed at analyzing the patterns of international law citations in the U.S. judicial system, as well as the role litigants and amici play in the process of judicial globalization. Utilizing an original dataset of international law citations in Supreme Court opinions, litigant and amicus briefs, we illustrated the importance of nonjudicial actors in transnational judicial dialogue. These actors, often the focus of judicial behavior literature, are seldom taken into consideration as active participants in international relations. Nevertheless, according to our results, they employ international legal authorities more frequently than judges. Furthermore, their engagement with international law prompts judges to consider them, significantly increasing the likelihood of international law citations in domestic court opinions.
Similarly, we turned our focus to the flow of citations of the U.N. Convention on the Rights of the Child, a widely popular international treaty which the United States has yet to ratify. While it is natural for transnational communication to attract attention when it takes place in the context of Supreme Court opinions – and especially landmark cases like Roper – we found that it was litigants and amici who first put forth argumentation based on the international treaty before American courts did, even if such arguments multiplied after Roper’s first national mention. Moreover, our analysis of the Convention’s citation patterns complements the quantitative analysis showing that nonjudicial actors are more active than judicial actors as participants in transnational dialogue.
Focusing on a selection of areas in which the provisions of the Convention were used by nonjudicial actors, we analyzed the path that arguments followed from litigant and amicus to state or federal judge, and from judicial mention in opinions to subsequent reiteration by litigants and amici. We treated the first instance of the U.S. Supreme Court relying on the Convention as a guiding doctrine for its decision, as the key event, and then investigated pre- and post-event citations to the Convention in state and federal litigation. In these issue areas, we found that pressures from below by litigants and friends of the court were more numerous and formed a significant aspect of judicial globalization. Additionally, we found that just like domestic law, international legal doctrine can be interpreted in varied ways and can be used as a footing to support opposing legal and policy outcomes. Cosmopolitan judges notwithstanding, judges are not as often well-versed or trained in international law; this is a legal area where they are likely to heavily rely on the instructive information offered by expert parties and trustworthy amici. The finding that nonjudicial actors are more likely to engage in transnational judicial dialogue and introduce such arguments to judges becomes all the more important if one considers the role that briefs traditionally play in filling information gaps. But because briefs are seldom policy-neutral and litigation is a costly, resource-intensive process where repeat players excel (Galanter Reference Galanter1974), those who do reach the courts and bring international law authorities and principles with them get to set the dialogue’s agenda. In this light, our findings indicate how court outputs that involve international law integration are more likely to reflect the specific preferences of lower parties, not unlike those observed in this study.
The expansion of transnational group networks, along with the increase in availability of foreign and international legal materials, combined with the reality of an interconnected world leaving its mark on American legal practice, suggests that such pressures will only intensify in the future, even for the most reluctant of participants in such a dialogue. For instance, this expansion is already occurring in legal areas that were untouched by the CRC in the past. In 2024, references to the Convention appeared in a Circuit Court of Appeals dissenting opinionFootnote 52 and two amicus briefsFootnote 53 involving transgender rights, as well as in an amicus briefFootnote 54 on the treatment of people experiencing homelessness. Remarkably, the dissenting judge in the aforementioned Circuit case signaled that a child’s right to have their gender on their birth certificate is protected by Art. 7 of the Convention, a doctrine that the state of Tennessee should adhere to. With the elected branches showing an inability or unwillingness to engage with international law, the judiciary will continue to converse with assistance from below.
Supplementary material
The supplementary material for this article can be found at http://doi.org/10.1017/S2045381725100130.
Funding statement
The authors have received no funding for this project.
Competing interests
The authors declare none.
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