Time for Codification? Tasking the ILC with Draft Articles on the Use of Force by States

[Dr Sergey Sayapin is Professor of Law at KIMEP University (Almaty, Kazakhstan)]

More than eighty years after the adoption of the Charter of the United Nations, the legal framework governing the use of force by States remains plagued by ambiguity. While Article 2(4) of the Charter lays down a general prohibition on the threat or use of force, and Articles 39 to 51 provide for limited exceptions, much of the law in this field has developed—and continues to evolve—through State practice and customary norms rather than through treaty law. In light of persistent contestation, interpretive disagreement, and geopolitical tension, the time may be ripe to consider a bold but overdue step: tasking the UN International Law Commission (ILC) with the preparation of Draft Articles on the Use of Force by States.

A Fragmented Legal Landscape

The UN Charter provides only a skeletal framework: a general prohibition (Article 2(4)), two express exceptions (Security Council authorisation under Chapter VII, and the inherent right of self-defence under Article 51), and certain vague principles such as sovereign equality and the duty to settle disputes peacefully. However, this architecture leaves many questions unanswered. Is anticipatory or preventive self-defence permitted under customary international law? What qualifies as an “armed attack” sufficient to trigger Article 51? Can humanitarian intervention ever be lawful absent Security Council authorisation? What status do doctrines such as the Responsibility to Protect (R2P) or “pro-democratic intervention” hold?

In the absence of authoritative interpretive guidance or a comprehensive codification effort, States have often interpreted the Charter’s provisions in self-serving or inconsistent ways. The result is a legal landscape shaped not by consensus, but by contestation.

Contemporary Uses of Force: The Legal Fog Persists

Since 2020, the world has seen a resurgence in the unilateral use of force, often accompanied by controversial legal justifications. In 2020, the United States and Iran exchanged tit-for-tat strikes across the Middle East, including the US strike on Qasem Soleimani in 2020 and Iran’s retaliatory missile attacks against US bases in Iraq. Russia’s full-scale invasion of Ukraine in February 2022—preceded by its 2014 annexation of Crimea—was defended by Moscow under the guise of collective self-defence of the Donetsk and Luhansk “people’s republics”, a claim widely rejected by the international community. Israel’s large-scale military operations in Gaza, including the 2023–2024 campaign following the Hamas attacks of 7 October 2023, have raised renewed debates about proportionality, necessity, and the legal limits of self-defence against non-state actors. 

In 2024, hostilities escalated significantly following Israel’s targeted killing of Iranian military advisers in Syria and Iran’s missile and drone strikes on Israeli territory, some of which were intercepted with US support. In June 2025, Israel—reportedly with US coordination—conducted targeted air and cyber operations against Iranian nuclear facilities, in a bid to prevent Iran from acquiring nuclear weapons capability. These acts were justified by reference to a doctrine of preventive self-defence, but received international criticism for lacking Security Council authorisation and for operating in legal grey zones.

Each of these incidents has been accompanied by diverging legal claims and counterclaims, underscoring the urgent need for authoritative guidance on the application of international law in this area. Without a clear and commonly accepted framework, the risk of escalation and erosion of the jus ad bellum regime becomes dangerously real.

Customary Law: The Invisible Constitution of Jus ad Bellum?

The importance of customary international law in this area cannot be overstated. Much of what governs the use of force today lies outside the text of the Charter, embedded instead in patterns of State behaviour, opinio juris, and the practice of international institutions. For instance, the ICJ in Nicaragua v. United States (1986) affirmed the continued relevance and separateness of customary law on the use of force. Yet, customary law’s unwritten and inductive nature often fuels legal uncertainty. Even leading cases—from Oil Platforms to Armed Activities on the Territory of the Congo—leave room for ambiguity. Clarifying the contours of these norms is not merely an academic exercise; it is a prerequisite for legal predictability, institutional legitimacy, and, ultimately, international peace and security.

The Case for ILC Engagement

The ILC is uniquely positioned to undertake such a clarifying and systematising endeavour. Its mandate—to promote the progressive development of international law and its codification—makes it the appropriate institutional forum to distil, articulate, and refine the principles governing the use of force. The success of past ILC projects such as the Articles on State Responsibility, the Draft Articles on the Protection of Persons in the Event of Disasters, and the Draft Principles on the Protection of the Environment in Relation to Armed Conflicts, demonstrates the Commission’s ability to navigate politically sensitive terrain with scholarly rigour and institutional legitimacy.

Draft Articles on the Use of Force by States could consolidate existing legal principles, clarify disputed doctrines, and provide guidance on emerging challenges such as cyber operations, the use of force by non-state actors, and the legality of interventions upon invitation. Moreover, a well-structured set of Draft Articles would serve as a reference point for domestic and international courts, regional organisations, and practitioners seeking clarity in complex legal disputes.

Relationship with the 1974 Definition of Aggression and the Rome Statute

A codification effort by the ILC would not occur in a legal vacuum. The 1974 Definition of Aggression, adopted by General Assembly Resolution 3314 (XXIX), offers a valuable starting point by identifying acts that may qualify as aggression. However, this definition was primarily intended for the UN Security Council’s political assessment, and was limited in scope.

Article 8 bis of the Rome Statute of the International Criminal Court builds upon the 1974 definition by criminalising the planning, preparation, initiation or execution of acts of aggression. However, it is framed in criminal law terms and addresses only the individual responsibility of political or military leaders. The proposed ILC Draft Articles would complement this by addressing State responsibility for unlawful uses of force, thus bridging the conceptual and normative gap between State responsibility and individual criminal accountability. Together, these instruments could form a more coherent legal architecture governing the use of force across both institutional and judicial dimensions.

What Might the Draft Articles Contain?

A future set of Draft Articles on the Use of Force by States would need to balance legal clarity with political feasibility. A preliminary outline might include:

1. General Principles

• Prohibition on the threat or use of force
• Peaceful settlement of disputes
• Sovereign equality and territorial integrity

2. Exceptions to the Prohibition

• Self-defence under Article 51 of the Charter
• Collective self-defence
• Security Council authorization

3. Contested Doctrines

• Anticipatory and preventive self-defence
• Humanitarian intervention and the “responsibility to protect”
• Interventions by invitation
• Protection of nationals abroad
• Pro-democratic interventions

4. Emerging Challenges

• Cyber operations as use of force
• Use of force by and against non-state actors
• Grey zone operations and hybrid warfare

5. Procedural Obligations and Safeguards

• Notification and reporting requirements (e.g. under Article 51)
• Thresholds for determining an “armed attack”
• Duty of proportionality and necessity

6. Legal Consequences of Unlawful Use of Force

• State responsibility and reparations
• Possible consequences for recognition, treaties, and diplomatic relations

7. Relationship with Other Bodies of Law

• Links with international humanitarian law
• Interaction with international criminal law (including Article 8 bis of the Rome Statute)

8. Final Provisions

• Application to States and international organisations
• Relationship with the UN Charter and other treaties

This structure could evolve through successive reports, State comments, and consultations. A possible end product might take the form of Draft Articles with commentaries, guiding principles, or even model clauses for future multilateral agreements.

Anticipating Objections

It is true that the politics of the Security Council and the strategic interests of powerful States will continue to shape real-world outcomes in this area. Some may argue that codification is futile in a domain so fraught with political discretion. But this view mistakes political contestation for legal irrelevance. The normative power of international law derives not only from enforcement, but from the ability to constrain conduct, shape expectations, and inform legitimate authority. A well-crafted set of Draft Articles would not eliminate controversy, but it could channel it within a clearer legal framework.

Furthermore, critics may suggest that the ILC has previously addressed elements of the use of force—particularly in its work on State responsibility or the immunity of State officials. Yet the Commission has never undertaken a comprehensive project dedicated specifically to codifying the substantive and procedural norms governing inter-State force. That lacuna is increasingly untenable in a world marked by hybrid warfare, proxy conflicts, and aggressive reinterpretations of the Charter’s provisions.

A Path Forward

To be effective, such a project must be carefully scoped. It might begin with a study group or working group to map existing rules and identify contested areas. Engagement with States, scholars, and practitioners would be critical throughout. The ILC might consider issuing guidelines or conclusions with commentaries in the first instance, leaving open the possibility of formal Draft Articles at a later stage. The goal would not be to rewrite the Charter, but to clarify its interpretation, articulate the status of parallel or supplementary rules under customary international law, and offer a coherent account of the rights and responsibilities of States when it comes to the use of force.

Conclusion

At a time when the international legal order is under significant strain, providing clarity and guidance on the most consequential aspect of international law—the use of force—is both urgent and necessary. Entrusting the ILC with the task of preparing Draft Articles on the Use of Force by States would not resolve all disputes, but it would mark a serious and constructive step toward reinforcing the rule of law in international affairs. The stakes could not be higher.