Dionísio Babo Soares*
International law is increasingly confronted with a paradox: the more sophisticated forms of coercion become, the less likely they are to trigger the legal regimes designed to regulate them. This raises a central question for the contemporary international order: how can international law continue to constrain and regulate abuses by States when they engage in hostile conduct without formally crossing the threshold of war?
The proliferation of activities in the so-called grey zone confirms that an increasing proportion of interstate coercion is deliberately designed to exploit areas of legal uncertainty, particularly regarding sovereignty, intervention, the use of force, and attribution, as noted by Michael N. Schmitt in Grey Zones in the International Law of Cyberspace. Although these legal frameworks remain formally intact, their effectiveness is increasingly tested by conduct specifically designed to exploit their thresholds of applicability, normative gaps, and evidentiary requirements.
At the heart of the problem lies the architecture of international humanitarian law, which is built upon thresholds of applicability. Its application depends upon the existence of an armed conflict, whether international or non-international. However, many contemporary forms of coercion are carefully calibrated to avoid crossing that threshold. Cyber operations, for example, may disrupt critical infrastructure, financial systems, and essential public services without causing physical destruction or producing the kinetic effects traditionally associated with armed conflict. Likewise, disinformation campaigns may destabilise societies and undermine democratic institutions without, in legal terms, constituting a use of force. In such circumstances, populations remain exposed to significant harm without benefiting from the protections afforded by international humanitarian law, revealing an increasingly pronounced disconnect between existing legal categories and contemporary operational realities.
Parallel challenges arise within the law of State responsibility. Although the principles governing the attribution of conduct are well established, their application becomes considerably more complex in situations characterised by indirect action and plausible deniability. The use of proxy actors enables States to project influence while formally distancing themselves from conduct that may constitute internationally wrongful acts, thereby complicating the demonstration of the effective control required under international law. In the cyber domain, the scholarly literature has consistently emphasised that while the applicable legal framework formally exists, its operationalisation faces significant challenges, particularly with regard to the legal characterisation of cyber activities and their attribution to States, issues comprehensively examined in the Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations. The consequence is not the absence of legal responsibility, but rather the practical weakening of its enforcement.
For least developed countries and small island developing States, these dynamics create a particularly acute structural tension. International law serves as an essential equaliser, providing smaller and more vulnerable States with a normative framework through which they can assert their rights and resist coercion. However, as grey-zone activities proliferate, these States confront a dilemma. Strict adherence to traditional legal categories risks rendering international law progressively irrelevant in addressing contemporary threats. Conversely, an overly flexible or expansive reinterpretation of legal rules may undermine the predictability and restraining function that constitute the very protective essence of international law. Ultimately, the process of adapting international law to emerging forms of conflict, if not undertaken with sufficient care, may itself erode the safeguards upon which vulnerable States most depend.
State practice demonstrates the urgency of this challenge. As Schmitt argues in Virtual Disenfranchisement: Cyber Election Meddling in the Grey Zones of International Law, cyber-enabled electoral interference exemplifies a domain of strategic legal exploitation precisely because the unlawfulness of such conduct, its gravity, and the range of legally permissible responses remain contested in several respects. However, such operations rarely reach the threshold of an “armed attack” under the Charter of the United Nations, thereby limiting the availability of the right of self-defence. Likewise, the use of non-State armed groups across various regional contexts illustrates how States may exercise strategic influence while simultaneously avoiding direct legal responsibility. Disinformation campaigns further exacerbate this reality by undermining governance and social cohesion without neatly fitting within existing legal regimes. Taken together, these practices demonstrate that the grey zone does not constitute a legal vacuum; rather, it is a space in which legal ambiguity is deliberately cultivated and strategically exploited.
In light of these developments, some commentators have advocated the formal recognition of the grey zone as an autonomous legal category. Such proposals, however, should be approached with caution. Codifying the grey zone risks institutionalising ambiguity and, in doing so, legitimising conduct that deliberately operates on the margins of legality. Rather than constraining opportunistic behaviour, formal recognition could encourage States to refine strategies specifically designed to remain within this sphere of legal indeterminacy. The strength of international law lies in its capacity to establish clear norms and legal limits; introducing a category defined precisely by its ambiguity would risk weakening that function. Accordingly, the grey zone should remain an analytical and strategic concept rather than a formal legal category.
A more constructive approach lies in strengthening the implementation of existing legal regimes through pragmatic and targeted measures. One priority is the development of more robust collective attribution mechanisms. Multilateral investigative bodies equipped with advanced technical expertise could help overcome the evidentiary challenges posed by cyber operations and proxy relationships. Joint attribution statements issued by groups of States or regional organisations could likewise enhance the credibility of attribution findings while reducing the political costs borne by States with limited capabilities. At the same time, greater clarification of the legal standards governing State responsibility for acts committed by non-State actors, including the interpretation of applicable control thresholds, would help strengthen international accountability.
Equally important is preserving the integrity of the legal regime governing the use of force. The threshold defining an “armed attack” should remain sufficiently high to ensure that the right of self-defence is not invoked in response to coercive acts of lesser intensity. Expansive doctrines, such as anticipatory or continuous self-defence, risk weakening the limitations embedded within the Charter system and may ultimately disadvantage the most vulnerable States, which depend upon clear and restrictive legal rules to constrain unilateral uses of force by more powerful States. Maintaining a disciplined interpretation of Article 51 of the Charter is therefore essential to preserving the balance between flexibility and restraint.
The role of international human rights law in responding to grey-zone activities is equally significant. The absence of armed conflict does not suspend States’ international legal obligations. On the contrary, international human rights law provides an essential normative framework governing State conduct in situations falling below the threshold of war. This is particularly important for vulnerable States, where domestic responses to hybrid threats—such as the expansion of surveillance powers or the adoption of emergency measures—may have disproportionate effects on fundamental freedoms. Ensuring that such responses remain consistent with international human rights standards is essential not only for protecting individuals but also for preserving the legitimacy of State action.
Finally, the role of international and regional institutions must be strengthened. The United Nations, through its competent organs—most notably the Security Council—as well as specialised fact-finding mechanisms and regional organisations, plays a central role in preventing, investigating, attributing, and responding to grey-zone activities. For least developed countries and small island developing States, which frequently lack the technical and institutional capacity to confront such threats independently, these mechanisms constitute indispensable sources of support. Strengthening their mandates, resources, and coordination capacities should therefore form a central component of any effective response.
Grey-zone conflict represents one of the defining challenges to the international legal order in the twenty-first century. It tests the capacity of international law to constrain the exercise of power in an environment characterised by plausible deniability, technological complexity, and strategic ambiguity. For vulnerable States, the implications are profound. Their security, sovereignty, and development prospects depend upon the continued relevance and effectiveness of a rules-based international order capable of responding to emerging forms of coercion without sacrificing its foundational principles. The way forward does not lie in abandoning existing legal frameworks or embracing conceptual innovations that may weaken them. Rather, it requires a careful process of reinforcement and adaptation: strengthening attribution mechanisms; preserving the integrity of the law governing self-defence; fully integrating the guarantees afforded by international human rights law; resisting the codification of ambiguity; and empowering multilateral institutions. Only through these measures can international law continue to fulfil its function as an instrument of equity, stability, and protection. For the most vulnerable members of the international community, this is not merely a matter of legal refinement; it is an indispensable condition for their survival in an increasingly contested international landscape.
*This article is intended exclusively for academic and educational purposes and does not represent the views of, nor bind, any institution with which the author is or has been affiliated.
