By Eric Vandenbroeck and co-workers

In the wake of intensifying international suspicion regarding Iran’s nuclear ambitions, in June 2025 United States conducted a series of precision bombings against three of Iran’s key uranium enrichment and related facilities. Employing the GBU-57 Massive Ordnance Penetrator, the most destructive bunker buster in its arsenal, the United States targeted facilities that had previously survived extensive Israeli air raids due to their deep underground fortification. The operation, while likely to delay Tehran’s nuclear program for several years (BBC, 2025), if not indefinitely, has raised fundamental questions about the evolving nature of international law and order.

The U.S. strikes were undertaken unilaterally, constituting a quintessential example of the unprovoked use of armed force against another sovereign state. In principle, such action is prohibited under customary international law and, more specifically, contravenes Article 2(4) of the United Nations Charter, which states: “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.” Yet, the context is complicated by Iran’s persistent refusal to allow on-site International Atomic Energy Agency (IAEA) inspections, thereby violating its obligations under both the IAEA Statute and the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).

Israel, perceiving an existential threat from Iran’s nuclearization—given Tehran’s longstanding hostility and history of direct and indirect attacks—initiated limited but substantial strikes based on its inherent right of self-defense under customary international law and Article 51 of the U.N. Charter. When these failed to neutralize the threat, the United States intervened directly, arguing that the necessity of self-defense justified its actions (Landay et. al, 2025).

This article does not seek to adjudicate the legal culpability of either the United States or Iran. Instead, it investigates why two foundational legal principles—the prohibition of the unprovoked use of force and the right of self-defense—have come into almost irreconcilable conflict in contemporary international politics. The analysis explores the international political impact of the U.S. operation on the existing legal order and considers the prospects for future developments in the international political-legal system.

 

The Classical Anarchical World and the Imperative for Self-Help

The international system, as currently constituted, is fundamentally anarchical. States operate in an environment devoid of any permanent, centralized authority capable of systematically enforcing legal rules. There is no international police force or universally competent court with the power to adjudicate disputes and enforce judgments. As a result, states are compelled to interpret international law for themselves, determining what constitutes a violation and what remedial measures are appropriate. This decentralized, horizontal structure means that the enforcement of international law is largely left to the discretion of individual states or coalitions.

International law itself is an unorganized amalgam of legal principles and partial arrangements designed to regulate specific regional or functional areas of international relations. While there are codified treaties and unwritten customary norms, these do not yet form a coherent, hierarchical legal system capable of consistent reasoning or authoritative interpretation. The result is a proliferation of opportunities for divergent, and sometimes contradictory, interpretations. In such an environment, self-help remains the only feasible recourse for a state seeking to ensure its survival or protect its vital interests when other states are either unwilling or unable to assist. This imperative for self-help is especially pronounced in situations involving the threat or use of force, where the stakes are existential and the margin for error is vanishingly small.

For unilateral uses of force, such as those undertaken by the United States and Israel against Iran, to be permissible under international law, they must be framed as acts of “anticipatory self-defense.” This doctrine, which emerged from the 19th-century Caroline incident, allows for preemptive action in the face of an imminent threat. The conditions are stringent: the necessity for self-defense must be “instant, overwhelming, leaving no choice of means, and no moment for deliberation,” and the response must be proportional to the threat.

The distinction between anticipatory self-defense and preventive war is critical. Anticipatory self-defense responds to an imminent attack, while preventive war seeks to forestall a potential, but not immediate, threat. The latter is generally considered unlawful under contemporary international law, as it lacks the requisite imminence and necessity. In the case of the U.S. strikes on Iran, the justification of anticipatory self-defense is highly contested. While the United States argued that Iran’s nuclear program posed an imminent threat, available intelligence suggested that Iran was not on the verge of acquiring a nuclear weapon (Davenport, 2025). Diplomatic and economic alternatives had not been exhausted, and the immediacy of the threat was not universally recognized. Thus, the action arguably failed to meet the strict criteria established by customary international law.

Moreover, the United States acted unilaterally, without seeking authorization from the U.N. Security Council or attempting to build a broad international coalition. This approach left the legal quality of the action uncertain, subject to post factum confirmation or rejection by the international community. Unilateral uses of force carry the risk of abuse, as states may invoke self-defense to advance their own interests rather than uphold widely accepted community values. Such practices, if unchecked, threaten the stability and legitimacy of the international legal order. Yet, the appeal of unilateral action persists, especially when collective mechanisms prove ineffective or unresponsive.

The decentralized nature of international law means that enforcement is often selective and inconsistent. While the U.N. Charter and other instruments provide for collective security and the peaceful resolution of disputes, the reality is that powerful states retain significant latitude to interpret and apply the law as they see fit. The lack of a universally competent enforcement mechanism means that violations often go unpunished, especially when perpetrated by major powers. This structural limitation is not merely a theoretical concern; it has profound practical implications. The inability of the international community to respond effectively to violations undermines the credibility of the legal order and encourages further breaches. In the case of the U.S. strikes on Iran, the absence of meaningful collective action or accountability mechanisms has left the legal status of the operation ambiguous, with potentially far-reaching consequences for the evolution of customary international law.

 

The Rise and Fall of the U.N. Collective Security System

The United Nations Charter, adopted in 1945, was designed to address the deficiencies of the interwar system and prevent the recurrence of catastrophic conflict. Article 2(4) prohibits the threat or use of force except in cases of self-defense or with the explicit authorization of the Security Council. The Council, composed of five permanent members (P5)—the United States, China, Russia, the United Kingdom, and France—and ten non-permanent members, was intended to provide a mechanism for collective security.

The effectiveness of the collective security system depends on the convergence of interests among P5. The veto power held by each permanent member ensures that the Council can act only when none of them objects. While this arrangement was designed to prevent unilateral action by any one power, it also means that the system is prone to paralysis when the interests of P5 diverge. The Council is fundamentally a political, rather than a judicial, body. Its decisions reflect the balance of power among the major states, and its legitimacy derives from the participation and acquiescence of its members. When the Council acts with the support or at least the abstention of P5, its decisions carry significant weight. When it is deadlocked, the system’s legitimacy and effectiveness are called into question.

The history of the Security Council is marked by periods of both effectiveness and dysfunction. During the Cold War, superpower rivalry often resulted in mutual vetoes and inaction. In the immediate post-Cold War period, U.S. predominance allowed for more frequent Council action, as Russia and China often acquiesced to U.S.-led initiatives. However, the resurgence of great power competition in the 21st century has rendered the Council increasingly dysfunctional. Russia’s annexation of Crimea in 2014 and its invasion of Ukraine in 2022, coupled with the growing alignment between Russia and China, have deepened divisions within the Council. The rise of the Global South and the increasing assertiveness of regional powers have further complicated the Council’s ability to act as an effective collective security mechanism.

Against this backdrop, the United States, under the Trump administration, opted for unilateral action against Iran, bypassing the Security Council and forgoing the formation of a “coalition of the willing.” The U.S. military possessed the unique capability to penetrate Iran’s fortified nuclear sites, but the operation entailed significant risks to international legitimacy and the integrity of the legal order. The failure of the Security Council to address major crises undermines its legitimacy and the broader international legal order. When powerful states act unilaterally, citing the ineffectiveness or paralysis of collective mechanisms, they set precedents that may be invoked by others in the future. The cumulative effect is the gradual erosion of the norm against the unilateral use of force and the weakening of the collective security system envisioned by the U.N. Charter.

The international legal assessment of the U.S. strikes on Iran remains unsettled, reflecting the enduring tension between the prohibition of the unprovoked use of force and the right of self-defense. The muted response of the international community suggests a degree of resignation, if not acceptance, of the new realities of power politics.

 

The Transition from U.S. Hegemony to a Global Balance-of-Power System

The post-World War II era was characterized by U.S. preponderance across economic, military, and ideological domains. The United States played a central role in constructing a liberal international order, anchored by institutions such as the United Nations, the World Bank, and the International Monetary Fund. This order incorporated an international legal system that sought to constrain the use of force and promote the peaceful resolution of disputes. The United States’ enforcement capacity lent credibility to the notion of an international rule of law, deterring potential challengers and conferring legitimacy on U.S.-led initiatives. The liberal international order pressed potential challengers to refrain from resorting to force, enabling the United States to manage global politics at relatively low cost.

Over the past two decades, the United States has experienced significant relative decline. The rise of China, the resurgence of Russia, and the increasing assertiveness of regional powers have eroded U.S. predominance. The “America First” policies of the Trump administration, coupled with growing domestic polarization, have further undermined the United States’ willingness and ability to act as the guarantor of the liberal international order. As U.S. hegemonic power has waned, the legitimacy and stability of the international legal order have come under increasing strain. The U.S. strikes on Iran, conducted without Security Council authorization and amid contested claims of imminence, would once have been unequivocally condemned as unlawful. Today, the absence of authoritative adjudication and the inability to impose sanctions on a permanent Council member leave the legal status of such actions ambiguous.

The current trajectory suggests a transition from U.S.-led unipolarity to a multipolar balance-of-power system. In this emerging order, several great powers—definitely the United States, China, Russia, and probably India, and possibly the European Union and Japan, and potentially a greater Israel—would exercise influence over distinct spheres. The mutual recognition of spheres of influence and the management of inter-civilizational fault lines would become paramount (Matsumura, 2025).

A global balance-of-power system operates through a multipolar check-and-balance mechanism. Each great power controls its own civilizational region, typically comprising smaller states. Despite constant friction along the fault lines, the system can sustain itself as long as the major powers respect each other’s essential spheres of influence (Matsumura, 2025). The U.S. attack on Iran can thus be seen as both a symptom and an accelerant of this systemic transition, as the established international legal order gives way to new patterns of power politics.

Abrupt transformations of international legal order are not without precedent. In 1918, President Woodrow Wilson’s Fourteen Points, including the principle of national self-determination, led to the dissolution of the Austro-Hungarian and Ottoman Empires and ended the Concert of Europe’s balance-of-power system. Similarly, the unconditional surrender and retroactive prosecution of war crimes at Nuremberg and Tokyo, championed by Presidents Roosevelt and Truman, transformed the laws of war and established new standards of accountability (Matsumura, 2025).

During the Cold War, the Soviet Union’s Brezhnev Doctrine, which justified armed intervention in socialist bloc countries, effectively modified the principle of territorial integrity. The doctrine was not invalidated due to Soviet veto power in the Security Council and the de facto acquiescence of other great powers. These examples illustrate how major shifts in the distribution of power can precipitate fundamental changes in the international legal order.

 

Implications for the International Legal Order

The U.S. strikes on Iran’s nuclear facilities exemplify the growing tension between the foundational principle of non-aggression and the perceived necessity of preemptive self-defense in an era of proliferating security threats. The operation’s unilateral character, the contestable imminence of the threat, and the tepid international response all point to a weakening of the norm against the unprovoked use of force. If such actions become normalized, the international legal order risks reverting to a system in which might makes right, and legal justifications are tailored to fit the exigencies of power politics. The collective security system envisioned by the U.N. Charter may be supplanted by a de facto acceptance of unilateral enforcement by major powers.

Customary international law evolves though the practice of states with opinio juris sive necessitatis (or opinion of right and necessity). The U.S. operation, and the international community’s reaction, may contribute to the emergence of a new norm permitting the use of force to prevent the acquisition of weapons of mass destruction by hostile states, even in the absence of clear imminence. This development would mark a significant departure from the post-1945 legal order and raise profound questions about the future of international law and the prospects for global stability.

With an emerging global balance-of-power system, the international community is departing from the principles of the U.N. Charter and collective security and seeing the emergence of a new, less constrained order in which power, rather than law, determines the use of force. This appears irreversible, although the outcome will depend on the willingness of states to defend the existing legal order, the effectiveness of collective mechanisms, and the evolving distribution of power in the international system.

 

Conclusion

The U.S. precision bombing of Iran’s nuclear facilities represents a critical juncture in the evolution of the international legal order. The operation highlights the enduring tension between the prohibition of the use of force and the right of self-defense, the limitations of the U.N. collective security system, and the challenges posed by the transition from U.S. hegemony to a multipolar balance-of-power system. While the immediate impact of the strikes may be to delay Iran’s nuclear ambitions, the broader consequence may be the erosion of foundational legal norms and the acceleration of systemic change in the world order. The muted international response suggests a growing acceptance of unilateral uses of force by major powers, with potentially far-reaching implications for the future of international law and global governance.

The choices made in response to the U.S. action against Iran will shape the trajectory of the international legal order for years to come, determining whether power, not law, will define the contours of world politics in the 21st century.

 

 

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