The US-Israel strikes on Iran which Israel described as a response to an ”existential threat”, raise a troubling question: Can States use force based on what might happen in the future? International law allows the use of force only in limited circumstances, such as self-defence. The United Nations (UN) Charter permits self-defence under Article 51 only “if an armed attack occurs,” a threshold long treated as central to the legality of force. It does not authorise force in response to threat in general, nor does it permit military action based on vague or future fears. The International Court of Justice (ICJ) has repeatedly held that only the gravest forms of force qualify as an “armed attack”. Not every unlawful act crosses that threshold.
Recent developments in West Asia suggest a shift in how States are interpreting the scope of self-defence under Article 51. At times, the focus turns to the possibility of a State acquiring the capability to carry out an armed attack. This moves the law from responding to attacks to anticipating them. If accepted, this would lower the legal threshold for the use of force.
The ICJ has repeatedly insisted on clear evidence of gravity and attribution before recognising a right of self-defence, as self-defence operates as a narrow exception within a broader prohibition on the use of force under Article 2 (4) of the Charter. The stability of the Charter depends on keeping that exception limited.
An armed attack is a concrete act of violence. An existential threat, by contrast, refers to what a State might be able to do in the future. International law has long debated whether Article 51 permits anticipatory self-defence. Some States accept that force may be used where an attack is imminent, drawing on the Caroline formulation that necessity must be “instant” and “overwhelming”. Even within that view, however, imminence is linked to concrete indicators of impending force. Preventive force, by contrast, addresses more distant or uncertain threats. However, the idea of using force against a remote or uncertain future threat has never been widely accepted under the Charter.
In its 1996 Nuclear Weapons opinion, the ICJ acknowledged that States have a basic right to survival. But it did not treat this as a separate legal basis for using force. Instead, it remained within the framework of Article 51, where the rules of necessity and proportionality continue to apply. Notably, recognising a right to survival is not the same as lowering the threshold for the use of force.
The issue, therefore, is whether the concept of an armed attack can be stretched to include threats that are neither actual nor imminent. If that happens, the legal threshold for self-defence becomes significantly lower.
Not every danger arrives as a sudden strike. Sometimes, it builds over time, as States deepen capabilities. That can be deeply unsettling. But it is not the same thing as an attack that is about to occur.
For countries such as India, which have long emphasised a narrow interpretation of self-defence under the UN Charter, such a shift would have serious legal and strategic implications. Expanding self-defence to include distant or speculative threats could weaken the rule against the use of force, which has long protected States from unilateral military action.
If States begin to use force based on what might happen rather than what has happened, the line between self-defence and preventive war starts to fade, allowing States to justify almost any action.
Jyoti Singh is a Delhi-based lawyer. The views expressed are personal
