Understanding Customary International Law: An Analysis of Nicaragua v. United States Case

1.0 INTRODUCTION

The Nicaragua case is widely regarded as a landmark decision of the International Court of Justice, featuring innovative reasoning on the genesis and observance of customary international law rules, seminal conclusions on the application of Article 51 of the ICJ on the use of force, as well as on a nation's fundamental right to self-defence. A plethora of scholarly articles on the Nicaragua v. United States (Merits) case, replete with cerebral expositions on the consequences of the judgment for public international law and the principles that govern international treaties, have been produced. For this essay, the focus will be on the State's actions and compliance with the principles of customary international law, evaluating these principles while noting the implications of the ICJ's position on the issue.

2.0 NATURE OF CUSTOMARY INTERNATIONAL LAW

The sources of international law consist of customs, general principles of law, and treaties. This is based on the text of Article 38(1) of the Statute of the International Court of Justice. Article 38 is akin to the provision in the Permanent Court of International Justice's (PCIJ) Statute, written in 1920 by a League of Nations-appointed Jurist Advisory Committee. The definition of custom in Article 38(1)(b) is "evidence of a general practice acknowledged as law" and has been referred to as "axiomatic" by the International Court of Justice (ICJ), as demonstrated in the Libyan Arab Jamahirya/Malta case.

Customary international law has been a key component of the global legal process for over two centuries, a dynamic process integrally intertwined with modern domestic legal systems. Each customary international law norm evolves over time as a result of repeated State actions. The element of repetition serves as the starting point for its creation. It is the recurrence of certain activities in similar situations that leads to the adoption of such practices as a "customary rule." Although the component of repetition may not occur in some circumstances, and the customary rule may arise due to a single precedent, most theorists assert that customary international law has two key components: (a) state practice and (b) opinio juris (sense of legal obligation). State practice is evident in positive and negative acts, as well as omissions. For the practice to be recognized internationally, it must be linked to international relations and consistent and often repeated. This was the ICJ's position in the Asylum case. However, international law does not prescribe a definitive timeline before practice is declared a valid customary rule. The generality of practice must be emphasized, according to several international law jurists, with state practice metaphorized as a customary rule being general rather than unanimous. This would imply that the practice underscores the views of most States. In the North Sea Continental Shelf Case, the ICJ emphasized the importance of "state practice" being broadly uniform. However, in Nicaragua v. United States (Merits), the court stated that strict adherence to the norm may not be necessary.

State practice includes administrative acts, judicial rulings, and state activities on international platforms, carried out by officials from governmental departments, state legal officers, courts, diplomatic agents, and political leaders. Until the early twentieth century, only the actions of persons or institutions authorized to articulate the State's view were counted. However, it has been noted that this view is no longer essential. Because international organizations act as separate legal entities with international personalities, the International Law Commission considers their cumulative practice as proof of State practice. The field should be expanded to include additional entities such as NGOs, international businesses, and individuals, according to Thirlway (2019) and Wood (2019).

Dahlman (2012) asserts that the psychological element of Opinio juris constitutes the second element of customary international law, which transforms a state practice into a legal custom. This factor represents the recognition of customary rules as legally binding by states, rather than as mere international morality or political considerations. Opinio juris also denotes the legal obligation of a customary rule, and a tacit agreement among states to recognize such rules as legal norms. Its significance lies in the fact that states engage in a variety of activities beyond their legal duties to demonstrate their generosity and to benefit their citizens.

Opinio juris thus serves as a critical differentiating factor in states' behavior, as it helps to separate customary international law from international morality or politics. The International Court of Justice (ICJ) recognized this in the North Sea Continental Shelf Case, where the frequency of a state's action was deemed insufficient to satisfy the requirement of a custom. States may engage in actions as a matter of courtesy or moral obligation, without a notion of legal obligation. However, implementing the practice solely based on legal conviction is insufficient, and other states should not oppose the conviction.

The existence of customary international law rules is derived from states' international practice, whether by taking affirmative actions or abstaining from taking action. While affirmative acts make proving the existence of a customary rule much simpler, the possibility of creating a customary rule of international law through the practice of abstention from action cannot be ruled out. This conventional rule of not acting in specific situations might lead to the establishment of legal standards of conduct. The elements of repetition, time, and consistency apply equally to abstention.

Despite its long-standing status as a key source of international law, customary international law remains riddled with intellectual and functional paradoxes, such as determining the existence of opinio juris and defining jus cogens customary standards. The issue of delineating customary international law has thus spawned a plethora of legal writings. The creation of customary international rule requires consistent practice by several states concerning a type of situation that falls within the domain of international relations, continued or repeated practice over a long period, the belief that the practice is required by or consistent with prevailing international law, and general acquiescence in the practice by other states.

States frequently view themselves as bound by treaty principles formed under customary international law, even if the treaties have not been ratified. For instance, the Convention on the Law of the Sea has resulted in new customary rules that have modified the 1958 Geneva Conventions. In the Lotus case, it was argued that the custom of states to refrain from prosecuting foreign citizens charged with causing collisions of vessels in the open sea constitutes a customary norm of international law.

In conclusion, the process of forming a customary rule of international law entails the development of a custom, which requires the recognition of such customs as legally binding by governments. Only when this recognition occurs can an international custom become an international law custom. Therefore, the formation of customary international law rules represents a distinct stage in the process of customary international law.

3.0 ANALYSIS OF THE NICARAGUA CASE AND ITS RAMIFICATIONS FOR CUSTOMARY INTERNATIONAL LAW

The Nicaragua case marks a pivotal starting point for any discussion on the emergence of the modern customary rule. The ICJ ruling in the Nicaragua case rested upon the bedrock of customary international law standards. Specifically, the case concerned the United States' military and paramilitary actions against Nicaragua between 1981 and 1984, following which the Nicaraguan government appealed to the ICJ to declare the US's actions in violation of international law.

The crux of the matter was that President Somoza's government was ousted in July 1979, paving the way for an administration established by the Frente Sandinista de Liberacion Nacional (FSLN). However, supporters of the former government and National Guard members opposed the new government. The US initially backed the new administration but shifted its stance upon learning that the Nicaraguan government was providing logistical support and weaponry to the El Salvadoran insurgents. Nicaragua contended that the US had organized and implemented measures against it, and that two groups had carried out armed actions against the new government. The first group, Fuerza Democratica Nicaragüense (FDN), operated along the border with Honduras, while the second group, Alianza Revolucionaria Democratica (ARDE), operated along the Costa Rican frontier. Early US funding for these anti-government groups (dubbed "contras") was clandestine. Nicaragua further maintained that the United States had effective control over the contras and had both developed and tactically directed their strategy and finances. Additionally, Nicaragua claimed that the United States military had carried out direct strikes against it with the intent of toppling its government. Strikes against Nicaragua included bombing its oil infrastructure, ports, and naval station, while US planes flew over the country gathering intelligence, delivering supplies to the contras on the ground, and intimidating the populace.

The US refused to recognize the ICJ's jurisdiction to decide the issue, and as a result, did not appear before the ICJ during the merit stages. Throughout the jurisdictional proceedings, the US claimed that it had acted in response to Nicaragua's aggression against Costa Rica, Honduras, and El Salvador based on an inherent right of collective self-defense established by Article 51 of the UN Charter. (Nicaragua v. United States (Merits), paras 126, 128).

However, in its final judgment on the merits, the ICJ held that the US had violated its customary international law obligation not to intervene in the affairs of another state (paras 191-201) when it financed, armed, and trained the contra forces (para 227), aided, supported, and encouraged the paramilitary and military activities against Nicaragua (paras 195, 230), and attacked Nicaragua directly in 1983 and 1984 (see paras. 187 – 201 of the Judgment). The Court also found that when the US ordered or permitted its aircraft to fly over Nicaragua's territory and placed mines in its interior and territorial waterways, the US violated its customary international law obligation not to infringe on another state's sovereignty.

The ICJ decision validated the application of the traditional bi-partite doctrine to determine the existence of an international customary rule or obligation, as stated in para. 183: "The Court has to next consider what are the rules of customary international law applicable to the present dispute. For this purpose, it has to direct its attention to the practice and opinio juris of States."

Charlesworth (1984-87) posited that the Court's judgment lacked application of the bi-partite doctrine and empirical enquiry into state practice. He contended that the Court's determination of the US's breach of customary international law did not necessarily negate the existence of an international customary norm, especially if the inconsistent state practices were treated as violations of the rule. Kirgis (1987), despite the lack of state practice supporting the alleged normative standards, emphasized that the Court's reliance on these prescriptive standards established customary international law principles barring the use of force.

In paragraph 186 of its decision, the ICJ acknowledged that the application of the rules in question might not have been perfect, but it did not believe that the practice must be in rigorous conformity with the rule for a customary norm to be established. Rather, the Court deemed it sufficient that state conduct should generally be consistent with such rules, and instances of inconsistent conduct should generally have been treated as breaches rather than indications of the recognition of a new rule. The Court confirmed that a State's conduct prima facie incompatible with a recognized rule but defended by appealing to exceptions or justifications within the rule itself confirmed rather than weakened the rule's significance.

Although some jurists disputed the logic of the Nicaragua case, arguing that it contained no verifiable evidence of the Court's theory on customary law rules and obligations, modern international law jurists agree that a customary international law rule accepted by a substantial number of nations is binding on all other states (Guggenheim, 1950; Kelsen, 2004; Arajarvi, 2016). Cassese (2016) emphasized that customary international law does not emerge through a purposeful legislative procedure like municipal laws but rather as a byproduct of states' behavior in international relations. Thirlway (2019) posited that the rules of customary international law can be considered as a "tacit agreement" by which States, by behaving in specific ways toward one another, agree to be guided by them in the future and to be legally bound by them.

It is worth noting that many international law principles and standards entail state pledges to refrain from specific activities in their relations with other nations. The respect of sovereignty concept requires states to desist from any action that violates another state's sovereignty. The principle of non-interference in the internal affairs of another country binds every state, thereby requiring them to refrain from meddling with another State's internal affairs.

On the other hand, Professor Verdross (1966) held a different view on this issue. He posited that international customary law could only be interpreted by the consent of States if a practice proving the existence of a rule of international law comprised the acts of every state bound by the Rule of Customary Law or if a State's rule of customary law is only binding when that State has participated in it. Verdross further noted that since customary international law rules are binding on any State, it must be shown by their actual behavior to demonstrate that all States have accepted these customary international law rules. Essentially, Verdross emphasized that international law must represent the reality of generally recognized State behavior, not just a narrow rule applying to a few nations.

4.0 CONCLUSION

In contemporary times, the legal notion of custom in international law has evolved to its most widely accepted definition, as found in Article 38(1) of the ICJ Statute (b). It is now commonly acknowledged that international customary law is a legally binding source of international law, recognized by governments worldwide. The binding nature of customary law is evident through its consistent application by both international and national courts and tribunals. The Permanent Court of International Justice (PCIJ) and the International Court of Justice (ICJ) have both affirmed the two fundamental components of custom: state practice or the objective element, and opinio juris or the subjective element. While the idea that a conventional norm of international law binds states juridically, irrespective of their recognition or approval of such a norm, has been challenged, particularly in the Nicaragua case, proponents and opponents of opinio juris have advanced similar arguments.

In conclusion, it is critical to highlight that the notion that customary international law rules recognized by a significant number of states are universally enforceable is not only misguided but also problematic in modern international law. Such a concept may be employed to justify the imposition of certain rules by a handful of states upon others. It is pertinent to note that customary international rules created by democratic western societies may not necessarily be acceptable to all Asian and African states. It is customary to establish the presence of universally acknowledged international law rules by examining universal practice and recognizing it as a rule of law. The number of states that have accepted such a rule of law is also considered. While it may be assumed that recognition by several state governments provides a basis for widespread acceptance, this is merely an assumption and not a conclusive verdict.

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