Arbitrary use of force will ultimately backfire

The US and Israel launched the military operation against Iran on February 28. The United States has repeatedly challenged international law with the Charter of the United Nations at its core, which will seriously undermine international peace and security and erode the authority of the international rule of law.

The Article 2(4) of the UN Charter clearly prohibit "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." This principle is considered as a fundamental principle of international law, and is agreed to belong to the jus cogens. In the field of international politics, the non-use of force principle serves as the cornerstone of the international order and represents the core values of the international community. Pursuant to the Charter, the use of force can only be justified on two grounds. One is where the state acts in self-defense individually or collectively "if the armed attack occurs" under the Article 51 of the Charter, the other is where the Security Council of the UN has authorized the use of force. However, as things stand, the United States' use of military force against Iran does not fall within the exceptions to the principle of prohibition of the use of force under international law, and the legal justifications put forward by the United States so far lack persuasiveness.

No sufficient evidence for invoking the right to self-defense

The exercise of the right to self-defense is subject to strict preconditions. The wording of the Article 51 of the Charter implies that the state can exercise the right of self-defense if it has sustained the armed attack. However, there is another way of interpretation by some states, indicating that the inherent right to self-defense as well as the Article 51 include the right to use force in anticipatory self-defense to prevent an imminent attack. The anticipatory self-defense can be traced back to the Caroline incident of 1837, where the US Secretary of State posited that the self-defense is possible when the "necessity of the self-defense is instant, overwhelming, and leaving no choice of means, and no moment for deliberation." However, a significant number of states do not accept this temporal widening of the right to self-defense, for example, Pakistan, Mexico and Turkiye.

In the vein of the theory of anticipatory self-defense, it requires an "imminent" threat of attack as a precondition. Among the states and the scholars who support the anticipatory self-defense, there is a common view toward a narrowly construed "manifestly imminent attack". This is mainly because the doctrine of anticipatory self-defense may go beyond the wording of Article 51 of the Charter. Without strict constraints, it could easily lower the threshold for the use of force, weaken the effect of Article 2(4) of the Charter, heighten the risk of conflicts, and run counter to the purposes and principles of international law to settle disputes by peaceful means.

In its Report on the Legal and Policy Frameworks Guiding the United States' Use of Military Force and Related National Security Operations 2016, the US reaffirms the condition of an "imminent attack", and sets forth factors to be considered in assessing whether such threat exists, including nature and immediacy of the threat, the probability of an attack and so forth. The US emphasizes the assessment of the "imminent attack" should be in corporate with the modern-day capabilities and technical innovations of the adversary, which will enable some flexibility in the assessment.

However, it is still not sufficient to determine whether there would be a manifestly imminent attack from Iran in the present case. In the letter to the UN Security Council dated March 10, 2026, the US relied much on the potential reconstitution of its nuclear program and the development of the ballistic missile production, while paid less attention to the more important factors, inter alia, the probability and the immediacy of the attack. As a matter of fact, in public domain, there is no evidence showing the intention and capability of Iran to attack the US and Israel. After the military operation last summer, President Trump publicly stated that the nuclear program of Iran was obliterated. It is also noted by some scholars that "no evidence was presented to show that since last summer somehow Iran reconstituted its programme, had the intent to build a weapon, put it on a ballistic missile, and then use it against the US or Israel." According to public reports, the US Senator Mark Warner disclosed that there was no intelligence indicating an imminent threat from Iran.

Moreover, in its letter dated March 10, the US also requested to consider all the "bad acts" of Iran since 1979 when assessing imminence. However, when assessing imminence, the most important factor would be the immediacy of the threat. Too much emphasis on the broader context of bilateral relations would lower the threshold for the exceptions to the prohibition on the use of force.

The attack from US and Israel is far from necessary. As ICJ has noted, self-defense "would warrant only measures which are proportional to the armed attack and necessary to respond to it." Some US scholars hold that in the present case, the armed attack from US and Israel is the "last window of opportunity" from the military perspective. In its letter dated March 10, the US also mentioned "peaceful measures have once again been attempted and exhausted." However, the negotiations were ongoing just before the attack, and negotiations were due to continue the following week with technical discussions. The diplomatic efforts had not been exhausted, the choice of use of force was not driven by the "last window" in the meaning of the necessity under international law, but more akin to be driven by the opportunity to launch the decapitation strike.

The 'on going armed attack' cannot justify the US armed action

In the letter of March 10, the US packs the conflicts between it and Iran as a "ongoing attacks and threats", and it implies that if the US was already in an ongoing armed conflict, it is not necessary to reassess whether an armed attack is imminent prior to the current action. Some scholars also indicate that it is not relevant whether or not Iran happened to present an imminent threat immediately prior to the attack when there is an ongoing conflict.

However, the jus in bello and jus ad bellum are distinct bodies of international law, and cannot be conflated. The former emphasizes all the activities during the armed conflict should be regulated by international law while the latter applies to assess whether the use of force is lawful or not. Despite this, there was no ongoing hostilities between US and Iran. In June 2025, the two states had reached a ceasefire, and thus the subsequent attack on Iran should be taken as a new attack.

The threshold of the collective self-defense has not been met

ICJ identified three requirements of the collective self-defense in Nicaragua case. First, there is at least one state that is entitled to take action by way of individual self-defense. Second, the victim state has to declare itself to be the victim before others are entitled to use of force. Third, the right of the state that is not the victim of armed attack relied on the victim state's request for assistance. However, in the letter of March 10, the US did not demonstrate whether Israel was the victim of the armed attack launched by Iran. The US claimed that Iran deploys proxies such as Hamas, Hizballah and the Houthis. However, it did not clarify how the actions taken by the non-state actors could legally be attributed to Iran.

Military operations by the United States and Israel against Iran have attracted widespread attention in international legal scholarship, as they raise critical questions concerning the interpretation and application of the prohibition on the use of force and the right to self-defense. Such operations bear not only on the authority and integrity of the international legal order centered on the UN Charter, but also on the durable peace and stability of the international community.

True security does not mean pursuing one's own security at the expense of others; rather, it requires pursuing common security on the basis of respect for the sovereignty and territorial integrity of all states. It calls for enhanced cooperation within the UN-centered international system, and for advancing a balanced, effective and sustainable security architecture through the interpretation, application and progressive development of international law.
The arbitrary use of force and the reckless lowering of the threshold for the use of force in pursuit of narrow self-interest may appear to yield short-term strategic advantages, but will ultimately backfire.

The author is a professor of Law, China Institute of Boundary and Ocean Studies, Wuhan University. 

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