The Current Crisis
The recurrent spectre of a United States–led blockade of the Strait of Hormuz has once again propelled into sharp relief the fragile equilibrium between the freedom of navigation and the imperatives of security. This narrow maritime artery, through which a substantial portion of the world’s energy supply transits, stands as a living testament to the enduring tension between openness and control that animates both the law of the sea and the broader architecture of international law. Any attempt to interdict passage through this chokepoint would not merely disrupt global commerce; it would raise profound legal questions as to whether such an act constitutes a lawful exercise of self-defence or an impermissible use of force under the contemporary legal order.
In this context, the discourse on blockade acquires renewed urgency, inviting comparison with analogous measures in the aerial domain, where the closure of airspace—though often less dramatic in its legal characterization—may produce consequences of comparable magnitude. The Strait of Hormuz thus becomes not only a geographic focal point but also a juridical crucible in which the competing claims of sovereignty, security, and global commons are tested with unsettling immediacy.
The concept of blockade of a seaway, viewed through the prism of contemporary international law, reveals an enduring tension between the primordial freedom of the seas and the exigencies of armed conflict. This dialectic, at once juridical and philosophical, finds its earliest coherent articulation in the doctrine of mare liberum, advanced by Hugo Grotius, who in the early seventeenth century proclaimed the seas to be incapable of appropriation and therefore open to all mankind. It is against this foundational premise that the notion of blockade must be critically examined, for blockade represents, in its essence, a deliberate derogation from the freedom of navigation—a principle now codified in the United Nations Convention on the Law of the Sea (UNCLOS) and regarded as one of the cornerstones of international maritime order.
The Two Types of Blockades
The law is seldom absolute, and nowhere is this more evident than in the uneasy coexistence of peacetime norms and wartime prerogatives. The distinction drawn between what is colloquially termed an “open blockade” and a “closed blockade” serves as an instructive entry point into this inquiry. Although these expressions lack formal codification, they encapsulate a functional dichotomy that has evolved through state practice. The so-called open blockade, or distant blockade, reflects the technological and strategic evolution of naval warfare. It is characterized not by the physical sealing of a coastline but by the projection of naval power across maritime spaces, often far removed from the immediate littoral. Surveillance systems, aerial reconnaissance, and long-range interdiction capabilities have rendered proximity less relevant, thereby enabling a belligerent to assert control over vast swathes of oceanic space. In contrast, the closed blockade evokes the classical imagery of warships stationed off an adversary’s ports, forming a tangible cordon that denies ingress and egress. This form, rooted in nineteenth-century naval practice, emphasizes immediacy and physical presence.
Teleology
Notwithstanding this distinction, the legal validity of either form hinges on the criterion of effectiveness, a principle deeply embedded in customary international law and reaffirmed in the San Remo Manual on International Law Applicable to Armed Conflicts at Sea. Effectiveness, in this context, is not a mere technical requirement but a normative safeguard against abuse. A blockade that exists only in proclamation, devoid of the enforcement capacity, is a legal nullity. This insistence on effectiveness serves to balance the belligerent’s right to wage war with the international community’s interest in preserving the integrity of maritime commerce.
The silence of UNCLOS on the subject of blockade is both conspicuous and instructive. As a treaty conceived in the milieu of peacetime governance, UNCLOS enshrines principles such as the freedom of navigation, innocent passage, and transit passage through international straits. These rights are articulated with a clarity and universality that reflect the collective aspirations of the international community. However, the drafters of UNCLOS were acutely aware of the limitations inherent in attempting to regulate wartime conduct within a peacetime framework. Consequently, the Convention abstains from addressing blockade, thereby leaving the matter to the lex specialis of armed conflict at sea.
This bifurcation of legal regimes underscores a fundamental truth: the law of the sea is not monolithic but context dependent. In times of peace, the principles of mare liberum prevail, ensuring that the seas remain a conduit for global interaction and economic exchange. In times of armed conflict, however, these principles are tempered by the imperatives of military necessity. The San Remo Manual, while not a binding instrument, represents a concerted effort to codify customary norms governing naval warfare. It delineates the conditions under which a blockade may be lawfully established, including requirements of declaration, notification, non-discrimination, and proportionality. Particularly noteworthy is the prohibition against the starvation of civilian populations, a reflection of the broader humanitarian ethos that has come to permeate international law.
An Act of War?
The question of whether a blockade constitutes an act of war invites a more nuanced analysis. Historically, the answer would have been unequivocal. The imposition of a blockade was tantamount to a declaration of war, triggering a cascade of legal consequences, including the rights and duties of neutral States. Neutral vessels breaching a lawful blockade could be captured, and their cargoes confiscated. This classical understanding, however, has been significantly altered by the advent of the United Nations Charter, which fundamentally reconfigured the legal architecture governing the use of force.
Article 2(4) of the United Nations Charter proscribes the threat or use of force against the territorial integrity or political independence of any state. Within this framework, a blockade—particularly one enforced through naval means—would prima facie constitute a use of force. Its legality, therefore, must be assessed against the exceptions provided by the Charter, namely self-defense under Article 51 and enforcement action authorized by the Security Council under Chapter VII. This shift from a permissive to a restrictive regime reflects the international community’s determination to curtail unilateral uses of force and to promote collective security.
The modern practice of States further complicates the analysis. The formal declaration of war has become an anachronism, supplanted by a spectrum of armed conflicts that may or may not be accompanied by explicit legal characterization. In this context, blockades may be instituted without a formal declaration of war, yet they retain their essential character as belligerent acts. The so-called “quarantine” imposed during the Cuban Missile Crisis is often cited as an attempt to circumvent the legal implications of blockade, yet its functional attributes were indistinguishable from those of a traditional naval blockade. This episode illustrates the elasticity of legal terminology and the extent to which States may seek to navigate the constraints imposed by international law.
At a deeper level, the concept of blockade raises profound questions about the balance between sovereignty and the common heritage of mankind. The doctrine of mare liberum posits that the seas are a global commons, accessible to all and subject to no single state’s dominion. Blockade, by contrast, represents an assertion of control that is inherently exclusionary. It transforms the sea from a space of openness into a theatre of contestation, where access is contingent upon the will of a belligerent power. This transformation is not merely physical but normative, as it entails a temporary reordering of legal priorities.
The tension between these competing paradigms is further exacerbated by technological advancements. The advent of long-range missiles, unmanned systems, and cyber capabilities has expanded the spatial and conceptual boundaries of blockades. An open blockade, conducted at a distance, may affect shipping routes far removed from the immediate vicinity of the conflict. This raises questions about the extent to which neutral States may be affected and the degree to which their rights under UNCLOS are curtailed. The principle of non-discrimination, as articulated in the San Remo Manual, seeks to mitigate these concerns by requiring that blockades be applied impartially to all vessels, irrespective of nationality. However, the practical implementation of this principle is fraught with challenges, particularly in complex geopolitical environments.
In this regard, the interplay between UNCLOS and the law of armed conflict at sea assumes critical importance. While UNCLOS does not explicitly address blockades, its provisions continue to inform the interpretation and application of wartime rules. For instance, the right of transit passage through international straits, a cornerstone of UNCLOS, may be subject to limitations in the context of a lawful blockade. The extent of such limitations remains a matter of legal debate, underscoring the need for a coherent and integrated approach to maritime governance.
The Humanitarian Aspect and Neutrality
The humanitarian dimension of blockade cannot be overlooked. The prohibition against starvation as a method of warfare, enshrined in the San Remo Manual and reflected in broader international humanitarian law, imposes a significant constraint on the conduct of blockades. This principle serves as a reminder that even in the exigencies of war, the rights and welfare of civilian populations must be safeguarded. The challenge lies in reconciling this imperative with the strategic objectives of a blockade, which may include the disruption of supply lines and the exertion of economic pressure.
It is also instructive to consider the implications of blockade for neutral States. The classical law of neutrality imposed strict obligations on neutrals, including the duty to refrain from assisting belligerents and the right to continue lawful commerce. Blockade disrupts this equilibrium by subjecting neutral vessels to inspection, diversion, or capture. The requirement of effectiveness, coupled with the obligation of notification, serves to ensure that neutrals are not arbitrarily deprived of their rights. Nevertheless, the potential for conflict remains, particularly in situations where the scope and enforcement of a blockade are contested.
Ultimately, the legal characterization of blockade as an act of war, or more precisely as a use of force, reflects the evolving nature of international law. The shift from a system that tolerated unilateral belligerent measures to one that prioritizes collective security and the rule of law represents significant normative development. Yet, the persistence of blockade as a tool of statecraft underscores the limitations of legal regulation in the face of geopolitical realities.
In synthesizing these considerations, one is struck by the enduring relevance of mare liberum as both a legal doctrine and a moral ideal. The freedom of the seas, while not absolute, remains a guiding principle that informs the development of maritime law. Blockade, in its various manifestations, constitutes a necessary but inherently problematic exception to this principle. Its regulation, therefore, demands a delicate balance between the imperatives of security and the preservation of a rules-based international order.
The discourse on blockade thus invites a broader reflection on the nature of international law itself. It is a system that aspires to universality yet must accommodate particularity; that seeks to constrain power yet cannot entirely escape its influence. In navigating this terrain, the jurist is called upon to engage not only with the letter of the law but with its spirit, to discern the underlying values that animate the legal order. In this endeavor, the legacy of Grotius and the enduring relevance of UNCLOS serve as both a foundation and a compass, guiding the ongoing quest for a just and equitable maritime regime.
My Take
Between Mare Liberum and Closed Airspace
The enduring vitality of mare liberum, as articulated by Hugo Grotius, lies not merely in its historical resonance but in its persistent capacity to illuminate contemporary tensions between freedom and control in domains that transcend territorial sovereignty. While Grotius spoke of the seas as incapable of occupation, a commons open to all, the modern jurist must confront the unsettling reality that both the oceans and the skies—though juridically distinct—are increasingly subject to episodic closure under the imperatives of security, conflict, and geopolitical rivalry. It is in this dialectic between openness and closure that one discerns both the continuity and divergence between the law of the sea and air law.
The seas, governed in large part by the United Nations Convention on the Law of the Sea, embody the Grotian ideal through the principle of freedom of navigation, particularly on the high seas. Yet, as earlier observed, this freedom is neither absolute nor immune from derogation. The imposition of a blockade—whether styled as open or closed—constitutes a paradigmatic interruption of mare liberum. It is, in essence, the temporary subjugation of a global commons to the strategic will of a belligerent. In contrast, the skies have never been subject to an equivalent doctrine of absolute freedom. From the inception of modern air law, codified in the Convention on International Civil Aviation (Chicago Convention) , the principle of complete and exclusive sovereignty of a state over the airspace above its territory has been axiomatic. Thus, while the seas begin from a presumption of openness, the skies begin from a presumption of closure, subject only to negotiated freedoms.
This fundamental distinction has profound implications when one considers the concept of an “act of war.” In the maritime context, a blockade has historically been regarded as an unequivocal belligerent act, now refracted through the legal lens of the United Nations Charter as a use of force under Article 2(4). The closure of maritime routes through blockade represents a direct challenge to the Grotian principle, justified—if at all—only under the narrow exceptions of self-defence or collective security authorization. The law, therefore, treats blockade as an extraordinary measure, requiring strict adherence to conditions such as effectiveness, proportionality, and humanitarian considerations, as reflected in the San Remo Manual on International Law Applicable to Armed Conflicts at Sea.
In the aerial domain, however, the closure of skies occupies a more ambiguous legal terrain. States routinely close their airspace for reasons that fall short of armed conflict: national security concerns, political disputes, or even public health emergencies. Such closures, while disruptive, are generally regarded as lawful exercises of sovereignty rather than acts of war. The distinction here is subtle yet significant. Whereas blockade is inherently coercive and directed outward, the closure of airspace is often framed as a defensive or regulatory measure, even when its effects extend beyond national borders.
The theoretical divergence between mare liberum and aerial sovereignty thus manifests in practice as a difference in legal thresholds. To close the seas through blockade is to cross the Rubicon into the domain of armed conflict, invoking the full panoply of the law of war. To close the skies, by contrast, may or may not rise to that level, depending on the context and intent. This asymmetry is not merely doctrinal but reflects the historical evolution of the two regimes. The seas, long a medium of commerce and exploration, demanded a legal order that facilitated openness. The skies, emerging later as a domain of strategic vulnerability, were quickly subsumed under the rubric of state control.
Yet, in practice, the boundaries between these domains are increasingly blurred. Consider, for instance, the naval “quarantine” imposed during the Cuban Missile Crisis. Although eschewing the terminology of blockade, the measure functioned as one, restricting maritime access and thereby constituting a de facto use of force. In the aviation context, the downing of civilian aircraft or the imposition of no-fly zones—often justified on security grounds—may similarly approach the threshold of armed conflict. The establishment of no-fly zones, in particular, represents a form of aerial interdiction that bears a conceptual resemblance to blockade, albeit within a different legal framework.
The closure of European airspace to certain carriers following geopolitical tensions provides a more contemporary illustration. While such measures are typically justified as sanctions or countermeasures, their cumulative effect is to fragment the global aviation network, undermining the cooperative ethos that underpins the Chicago Convention. Unlike blockade, these closures are rarely characterized as acts of war, yet they may have comparable economic and strategic consequences. This divergence in characterization underscores the elasticity of legal concepts and the influence of political considerations in their application.
From a jurisprudential perspective, the interplay between mare liberum and aerial sovereignty invites a re-examination of the concept of the global commons. If the seas are to remain open except in the most exigent circumstances, should not the skies, as conduits of global connectivity, be accorded a similar status? Conversely, if states may lawfully close their airspace with relative ease, does this not erode the normative force of openness in the maritime domain as well? These questions are not merely academic but bear directly on the future of international law in an era of increasing fragmentation.
The concept of an act of war, too, requires careful calibration. In the contemporary legal order, shaped by the UN Charter, the emphasis has shifted from formal declarations to the substantive nature of the act. A blockade, by virtue of its coercive and exclusionary character, readily qualifies as a use of force. The closure of skies, however, occupies a spectrum that ranges from benign regulatory action to de facto belligerency. The challenge lies in distinguishing between these modalities and ensuring that the legal framework remains responsive to evolving realities.
In both maritime and aviation contexts, examples abound that illustrate the tension between theory and practice. The enforcement of blockades in regional conflicts, often accompanied by disputes over their legality, reveals the fragility of the normative constraints imposed by international law. Similarly, the proliferation of airspace restrictions, whether in response to conflict or political disagreement, highlights the discretionary power of states and the limitations of existing regulatory mechanisms.
Ultimately, the juxtaposition of mare liberum and the closure of skies serves as a reminder of the dynamic and contested nature of international law. It is a field in which principles and practice are in constant dialogue, each shaping and reshaping the other. The Grotian vision of an open sea continues to inspire, even as it is challenged by the realities of power and conflict. The sovereignty of the skies, while firmly entrenched, is increasingly subject to pressures that demand greater openness and cooperation.
In my view, the task of the contemporary jurist is not merely to reconcile these competing paradigms but to transcend them, crafting a legal order that accommodates both the necessity of security and the imperative of connectivity. This requires a nuanced understanding of the concept of an act of war, one that recognizes its evolving contours and its implications across different domains. It also demands a renewed commitment to the principles of fairness, proportionality, and humanity that underpin international law.
Thus, the discourse on blockade and the closure of skies is not an isolated inquiry but part of a broader reflection on the nature of global governance. It challenges us to reconsider the balance between freedom and control, between sovereignty and commonality, and between law and power. In this endeavor, the legacy of Grotius and the frameworks established by UNCLOS and the Chicago Convention remain indispensable, guiding us toward a more coherent and equitable understanding of the spaces that connect us all.
