Introduction
Article 2(4) of the United Nations (UN) Charter stands as the cornerstone of the modern international legal order, prohibiting the threat or use of force in international relations. Conceived from the devastation of two world wars, its purpose was to usher in an era where disputes are settled peacefully and sovereign equality is respected. However, the history of international relations since 1945 presents a starkly different reality. This paper will argue that despite its status as a norm of customary international law, the enforcement of Article 2(4) has been profoundly ineffective. This ineffectiveness is not due to ambiguity in the law itself, which has been clarified by the International Court of Justice (ICJ), but rather a consequence of the political structure of the UN, particularly the veto power of the permanent members of the Security Council. Through an analysis of decided cases and instances of state practice, this paper will demonstrate that while the prohibition on the use offorce is clear in principle, its enforcement is selective and ultimately fails when confronted by the geopolitical interests of powerful states.
The Charter's Prohibition on the Use of Force
The UN Charter establishes a comprehensive system for the maintenance of international peace and security. At its heart lies Article 2(4), which dictates that "All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations" (United Nations, 1945). This prohibition is fundamental and intended to be near-absolute, with only two explicit exceptions provided within the Charter itself.
The first exception is the "inherent right of individual or collective self-defence" under Article 51, which is permissible only "if an armed attack occurs against a Member of the United Nations". The second exception is military action authorised by the UN Security Council (UNSC) under Chapter VII. According to Article 39, the UNSC has the authority to determine the existence of any "threat to the peace, breach of the peace, or act of aggression" and to take measures to restore international peace and security. These measures can include sanctions under Article 41 or, ultimately, the use of armed force under Article 42. This framework creates a system of collective security where the unilateral use of force is outlawed, and the legitimate use of force is monopolised by the Security Council, acting on behalf of the international community. In principle, this provides a clear legal and institutional mechanism for enforcing the prohibition in Article 2(4).
The Role of the ICJ: Clarifying the Law but Lacking Enforcement Power
The International Court of Justice has played a significant role in affirming and clarifying the scope of Article 2(4). The Court’s jurisprudence confirms that the prohibition is not merely a treaty obligation but also a rule of customary international law, binding on all states. The seminal case in this regard is the Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America) (1986). The ICJ found that the United States' actions in training, arming, and funding the Contra rebels in Nicaragua constituted a breach of the prohibition on the use of force and an unlawful intervention in the affairs of another state. The Court famously stated that the principle of the non-use of force is a "cornerstone of the United Nations Charter" (ICJ, 1986, para 190).
However, the Nicaragua case is also a primary example of the system's enforcement failure. The United States refused to recognise the ICJ's jurisdiction and boycotted the merits phase of the proceedings. After the judgment was delivered, Nicaragua turned to the UN Security Council to enforce it. The US, as a permanent member, promptly vetoed the draft resolution that called for full compliance with the Court’s decision (Schwebel, 1987). This demonstrated a fundamental weakness: a P5 member could violate a core tenet of international law, be condemned by the world's highest court, and then use its political power within the UNSC to block any consequences.
Later cases have reinforced the ICJ's legal interpretation while simultaneously highlighting the limits of its power. In Oil Platforms (Islamic Republic of Iran v. United States of America) (2003), the Court scrutinised the US claim of self-defence for its attacks on Iranian oil platforms, finding that the actions did not meet the criteria of necessity and proportionality. Similarly, in Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda) (2005), the ICJ found that Uganda's military intervention in the DRC constituted a grave violation of Article 2(4). While these judgments provide legal clarity and a formal condemnation of unlawful uses of force, their practical impact is limited. They do not reverse the effects of the illegal force, and the process of securing reparations, as seen in the DRC case, can be arduous and subject to political negotiation, further underlining the gap between legal ruling and effective enforcement.
State Practice and the Paralysis of the Security Council
The most compelling evidence for the non-effective enforcement of Article 2(4) comes from state practice, where the political realities of the international system frequently override legal obligations. The UNSC, designed to be the ultimate enforcer, is often paralysed by the veto power held by its five permanent members (China, France, Russia, the United Kingdom, and the United States). As Christine Gray (2018) notes, the collective security system was never intended to be used against a permanent member or a state under its protection.
This structural flaw has been evident throughout the UN's history. During the Cold War, the ideological divide between the US and the USSR led to frequent vetoes, preventing the UNSC from taking decisive action on many occasions. The post-Cold War era brought hopes of a more cooperative security environment, but these were soon challenged. The NATO intervention in Kosovo in 1999, undertaken without UNSC authorisation, is a key example. It was justified by proponents on moral grounds of humanitarian intervention to prevent ethnic cleansing, but it was technically an illegal use of force under the Charter framework, as Russia would have vetoed any authorisation (Cassese, 1999). This created the controversial precedent of an "illegal but legitimate" use of force, undermining the Charter’s authority.
The 2003 invasion of Iraq led by the United States and the United Kingdom further eroded the Article 2(4) regime. The legal justification, based on a contentious interpretation of prior UNSC resolutions and a doctrine of pre-emptive self-defence, was widely disputed and failed to gain explicit authorisation from a deeply divided Security Council (Lowe, 2003). More recently and perhaps most starkly, Russia's 2014 annexation of Crimea and its full-scale invasion of Ukraine in 2022 represent blatant violations of Article 2(4). In both instances, Russia's position as a permanent member of the Security Council has allowed it to veto any substantive resolution condemning its actions or authorising enforcement measures, rendering the body powerless to fulfil its primary mandate. These events show that when a permanent member chooses to use force, the enforcement mechanism of the Charter simply ceases to function.
Conclusion
The prohibition on the threat or use of force enshrined in Article 2(4) of the UN Charter remains a central normative principle of international law. The jurisprudence of the ICJ, particularly in the Nicaragua case, has affirmed its status as a fundamental rule of both treaty and customary law. However, the system designed to enforce this rule is critically flawed. The legal pronouncements of the ICJ are rendered impotent when a powerful state refuses to comply, and the Security Council, the designated enforcer, is consistently paralysed by the political self-interest of its permanent members and their use of the veto.
The decided cases clarify the law, but the reality of state practice, from Kosovo to Iraq and Ukraine, demonstrates a persistent and troubling gap between legal principle and political reality. The enforcement of Article 2(4) is not non-effective because the law is unclear, but because the political will and the institutional capacity to apply it universally and impartially are absent. Consequently, the collective security system envisioned in 1945 remains an ideal rather than a reality, effective only when the interests of the world's most powerful states align, or when the transgressor is a state with no powerful allies. Until this fundamental structural problem is addressed, the enforcement of Article 2(4) will remain selective, contingent, and ultimately ineffective in the face of determined aggression by major powers.
References
Cassese, A. (1999) 'Ex iniuria ius oritur: Are We Moving towards International Legitimation of Forcible Humanitarian Countermeasures in the World Community?', European Journal of International Law, 10(1), pp. 23-30.
Gray, C. (2018) International Law and the Use of Force. 4th edn. Oxford: Oxford University Press.
International Court of Justice (ICJ) (1986) Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Merits, Judgment, ICJ Reports 1986, p. 14.
International Court of Justice (ICJ) (2003) Oil Platforms (Islamic Republic of Iran v. United States of America), Judgment, ICJ Reports 2003, p. 161.
International Court of Justice (ICJ) (2005) Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda), Judgment, ICJ Reports 2005, p. 168.
Lowe, V. (2003) 'The Iraq Crisis: What Now?', International and Comparative Law Quarterly, 52(4), pp. 859-871.
Schwebel, S. M. (1987) 'The Treatment of Human Rights and of the Principle of Non-Intervention in the International Court of Justice', Proceedings of the Annual Meeting (American Society of International Law), 81, pp. 493-497.
United Nations (1945) Charter of the United Nations.
