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Unpacking Jus Ad Bellum Proportionality And Examining Its Relationship With The Jus In Bello In Light Of The Equal Application Principle, Jared Dass

International Law Studies

The jus ad bellum is one of the most important areas of international law, with the prohibition on the use of force forming the cornerstone of the UN Charter. However, a lack of doctrinal clarity, especially regarding the jus ad bellum proportionality principle, undermines its ability to meaningfully regulate the use of force by States in self-defense. There is further lack of understanding as to how the jus ad bellum interacts with the jus in bello, in particular as between the two proportionality principles found in both bodies of law. The orthodox view rejects any such interaction, for fear …

Military Ai And The Specter Of The Limitless War, Yuval Shany, Yahli Shereshevsky

International Law Studies

Legal and extra-legal factors related to the development of international humanitarian law (IHL) support the exercise of strategic restraint during armed conflicts. We claim, however, that technological developments in the area of military artificial intelligence (AI) fundamentally do away with many of the technological constraints that limited the capacity of militaries to fully utilize the “license to kill” afforded to them by IHL. Such a violence-enhancing effect can become even more dramatic in cases where other restraining factors are less effective. The upshot of our analysis is that the implicit assumption that IHL would be applied in a context of …

Symposium—Introduction, Russell Buchan

International Law Studies

In March 2025 the University of Reading and the U.S. Naval War College convened a workshop at the University of Reading in the United Kingdom to examine the application of the jus ad bellum, jus in bello, and international criminal law to the use of military AI. This is the introduction to the symposium, published as Volume 107 of International Law Studies.

Assessing The Role Of Ai In Determining The Necessity And Proportionality Of The Exercise Of Self-Defense Against An Armed Attack, Marco Roscini

International Law Studies

This article explores whether artificial intelligence (AI) constitutes an asset or rather a challenge in assessing the necessity and proportionality of a State’s response to an armed attack in the context of self-defense. Two central arguments are advanced. First, while AI may assist in detecting incoming threats of armed attacks, abstract and highly context-driven notions like necessity and proportionality would be very difficult to encode into algorithms. Second, even assuming that this were possible, relying on AI to determine the necessity and proportionality of a self-defense response would present as many challenges as it does advantages and, therefore, should be …

Artificial Intelligence And The Prohibition On The Use Of Force: Intention And Causation, Russell Buchan

International Law Studies

This article explores the application of Article 2(4) of the United Nations Charter to AI-enabled systems that carry out unintended engagements involving the use of force. First, it analyzes whether State responsibility for a breach of the prohibition on the use of force is defined in subjective or objective terms. Most commentators maintain that a State must intend to use force against the victim State in order for the prohibition to apply. However, through an examination of State practice, this article demonstrates that the prohibition is based on objective responsibility. Second, this article assesses whether a State must cause the …

Artificial Intelligence And The “Armed Attack” Threshold In International Law, Katie A. Johnston

International Law Studies

This article argues that the deployment of artificial intelligence, even in its strong fully autonomous form, does not have significant consequences for the application of the jus ad bellum framework, and in particular the armed attack threshold. As with all new weapons technologies, the deployment of artificial intelligence in the resort to force requires consideration of what “imminence” means in this context. However, artificial intelligence is fundamentally a means of making decisions to resort to force or contributing to the reasons for which such decisions are made by humans. Unlike the jus in bello, the jus ad bellum is …

Classification Of The Armed Conflicts In The Near East, Marco Sassòli

International Law Studies

This article explores the proper classification of Israel’s current conflicts with Hamas and Hezbollah as international or non-international armed conflicts. It discusses the different possibilities of how the international humanitarian law of international or non-international armed conflict applies to those conflicts and whether and to what extent the international humanitarian law of military occupation applies to the conduct of Israel Defence Forces in the Gaza Strip and Lebanon. It also explains why the proper classification of the conflicts still matters and is not only an intellectual exercise for scholars or students. While every conflict has its specifics, the article deals …

Iran And Its Proxies: Attribution And State Responsibility, Jennifer Maddocks

International Law Studies

Iran has invested heavily in proxy militias since the regime's founding in 1979. In the decades that followed, groups such as Hezbollah in Lebanon, Shi'a militias in Iraq and Syria, and the Houthis in Yemen have projected Iran's influence across the region. Today, Iran's proxy network is considerably weakened due to Israel's military actions following October 7, 2023, and the fall of the Assad regime in Syria. Yet the Houthis' attacks on Israel and against Red Sea shipping demonstrate how Iran's support to these groups continues to facilitate their conduct in violation of international law. This article examines Iran's potential …

Cosmic Force: A Framework For Applying The Prohibition Of The Use Of Force In Outer Space, Erin Pobjie

International Law Studies

Outer space is becoming increasingly contested and existing approaches to identifying prohibited force in outer space lack a systematic foundation, hindering their application to novel challenges such as temporary interference with critical satellites or threats involving commercial space actors. This article addresses this gap by developing the first comprehensive, multifactorial legal framework for identifying a prohibited use of force in outer space. This framework provides a structured method for analyzing non-kinetic actions, temporary effects, and persistent hazards like space debris. It fundamentally advances existing legal approaches in three ways. First, it establishes when States can be implicated in a violation …

What Are “Wartime Authorities” And When Can The President Use Them? An Expert Q&A, Tess Bridgeman, Rebecca Ingber, Scott Roehm

Online Publications

The first several months of President Donald Trump’s second administration have been marred by the chaotic and often unlawful use, or threatened use, of wartime and terrorism-related authorities for what are essentially domestic immigration or criminal law enforcement purposes. This is not the first time a president has sought to push the boundaries of his wartime powers, or outright claimed those he did not have, but it may well be the most extreme. Indeed, Trump’s reliance on wartime authorities in contexts entirely divorced from armed conflict, or even the threat of force against the United States, puts the country on …

The Special International Peace Zone: From History, Through Practice, Toward An End To Armed Conflict In Ukraine, Tom W. Bell

Notre Dame Journal of International & Comparative Law

This paper presents the special international peace zone as both an observed and ideal institution. Such a zone quells military conflict in an area over which sovereigns make conflicting territorial claims. It operates through an interim administration, governed by its own rules, independent of any single sovereign. Past examples include the Free City of Danzig (1920-39), the Free Territory of Trieste (1947-54), and United Nations Interim Administration Mission in Kosovo (1999-2008). Despite proven successes, these zones have suffered from an undue reliance on multi-national organizations—first the League of Nations and now the United Nations. Warring sovereigns seldom agree about the …

Maritime Incidents In The South China Sea: Measures Of Law Enforcement Or Use Of Force?, Aurel Sari

International Law Studies

China has sought to extend its control over the South China Sea at the expense of neighboring countries. In pursuing its goals, Beijing adopts a “power and law” approach, claiming extensive territorial and maritime rights in contravention of the UN Convention on the Law of the Sea and asserting these rights through coercive action in disputed waters. A key element of China’s strategy involves the use of coast guard and maritime militia vessels in an effort to portray its operations as measures of law enforcement, rather than displays of coercive power.

This article argues that the Chinese narrative of law …

Narrowing “The Gap”: Counter Gray Zone Operations, Raul (Pete) Pedrozo

International Law Studies

China is exploiting "The Gap" by conducting provocative Gray Zone operations to challenge its neighbors' sovereignty and sovereign rights, as well as their navigational rights and freedoms, in waters off their coast in the East China Sea, Taiwan Strait, and South China Sea. By engaging in malign activities that fall below the threshold of an "armed attack," China anticipates it can incrementally advance its interests without eliciting a military response from the targeted States. Diplomatic protests and third-party dispute settlement have not convinced China to halt its aggressive behavior. This article suggests States should use non-lethal counter-piracy tactics, techniques, and …

The Defense Of Taiwan: Possible Legal Justifications, Raul (Pete) Pedrozo

International Law Studies

This article examines four possible interconnected legal arguments that can be used by the United States and its allies and partners to justify the defense of Taiwan in the event of a Chinese invasion of the island. First, the United States could recognize Taiwan as an independent nation. Second, the three joint communiqués between the United States and China are premised on an understanding that the Taiwan issue will be resolved by “peaceful” means. A Chinese invasion of Taiwan would certainly breech that understanding and allow the United States to recognize Taiwan as a sovereign State. Third, a Chinese invasion …

Cyberspace And The Jus Ad Bellum: The State Of Play, Michael N. Schmitt, Anusha S. Pakkam

International Law Studies

This article examines how States are interpreting one aspect of the international law governing cyber activities, the jus ad bellum. The article focuses on two issues: (1) the prohibition on the use of force found in Article 2(4) of the UN Charter, and (2) the right of self-defense in Article 51. The critical unsettled question regarding the first issue is the threshold at which a hostile cyber operation can be characterized as a “use of force” subject to the prohibition of Article 2(4). Concerning the second issue, a number of unresolved questions plague the application of the right of …

“Unwilling Or Unable”, Lucy V. Jordan

International Law Studies

Critics of the unwilling or unable doctrine suggest that it could undermine the United Nations collective security system and argue that it requires an unacceptable ceding of a State’s territorial sovereignty. Increased reliance on the doctrine following the terrorist attacks of 9/11, particularly in relation to the use of force against ISIL in Syria since 2014, has caused the doctrine to face significant scrutiny. The purpose of this article is to ascertain whether the unwilling or unable doctrine has reached customary international law status. If found to be the case, the doctrine would confirm the right of States to act …

Re-Imagining The Post-9/11 Authorizations For Use Of Military Force In The Era Of Emerging Consensus On Reform, Peter J. Amato

Journal of Legislation

No abstract provided.

The Lessons Of 9/11 For October 7, Mary Ellen O'Connell

NDLS in the News

October 7 is being called Israel’s 9/11. The comparison is apt for the lessons that can be learned as to the legality of launching a ground offensive to respond to terrorism.

Aid And Assistance As A “Use Of Force” Under The Jus Ad Bellum, Michael N. Schmitt, W. Casey Biggerstaff

International Law Studies

Although the prohibition of the use of force is a cornerstone of international law, our understanding of what constitutes a “use of force” under Article 2(4) of the UN Charter nonetheless continues to evolve. While the term was traditionally understood to mean armed force, emerging interpretations are expanding our understanding of the prohibition’s breadth. The Charter’s text, travaux préparatoires, and subsequent interpretations and practice by States, reinforced by the persuasive reasoning of the International Court of Justice, all confirm that the notion of force extends to indirect force, which includes military support provided to parties to a conflict. Yet, to …

Twenty Years Of Drone Attacks, Mary Ellen O'Connell

NDLS in the News

On November 2, 2002, the United States conducted its first targeted killings using a drone. CIA agents based in Djibouti launched the drone’s two Hellfire missiles at a vehicle traveling in rural Yemen, killing six...

Some Reflections On The Threshold For International Armed Conflict And On The Application Of The Law Of Armed Conflict In Any Armed Conflict, T.D. Gill

International Law Studies

This essay discusses the threshold of application of international humanitarian law (IHL) in both international (IAC) and non-international armed conflicts (NIAC). In relation to IAC it questions whether the International Committee of the Red Cross (ICRC) “first shot” approach is the most appropriate, since it opens the way for the intensification of conflicts beyond what is necessary in relation to relatively minor armed incidents and argues that the humanitarian protection clauses of IHL should be separated from the rules governing hostilities and makes a case for the application of ad bellum considerations of necessity and proportionality to act as a …

The Prohibition On Intervention Under International Law And Cyber Operations, Ori Pomson

International Law Studies

Given that cyber technologies have made way for attempts to influence the affairs of other States in novel and unique ways, scholars have turned to the international legal rule which is prima facie most relevant in addressing such meddling; namely, the prohibition on intervention. Moreover, there appears to be quite a wide-ranging consensus in scholarship that the prohibition on intervention applies to a broad range of cyber operations. In contrast to such scholarship, this article argues that, under the lex lata, the prohibition on intervention only applies to acts amounting to a use of force or constituting support for …

Understating The Double-Standard On The Use Of Force, Mary Ellen O'Connell

Journal Articles

In the days following the start of Russia's full-scale invasion of Ukraine on 24 February 2022, (1) international law organization leaders issued unprecedented statements of condemnation. (2) No other world event has led to so many consistent expressions from these groups respecting a violation of international law. The occasion merited the response. Russia's invasion was only the second time a member of the United Nations has attempted to conquer and eliminate another UN member since the adoption of the UN Charter in 1945. The first time was in August 1990, when Iraq invaded Kuwait. (3) At that time, the world …

Revisiting Ad Bellum Proportionality: Challenging The Factors Used To Assess It, Yishai Beer

International Law Studies

Traditionally, international law has established a binary distinction between jus ad bellum and jus in bello. The former relates to the right to exercise military force. The latter regulates the conduct of adversaries engaged in an armed conflict. However, the prevailing legal approach doesn't accept this dichotomy. It wants to reduce war's hazards by applying the ad bellum rules, including the proportionality requirement, continuously throughout the conduct of armed conflict. To that end, it has established factors that define the essence of the continuing ad bellum proportionality requirement. This article challenges the near-unanimous consensus regarding these factors. It argues that …

Military Action To Recover Occupied Land: Lawful Self-Defense Or Prohibited Use Of Force? The 2020 Nagorno-Karabakh Conflict Revisited, Tom Ruys, Felipe Rodriguez Silvestre

International Law Studies

In September 2020, heavy fighting erupted between Armenia and Azerbaijan in and around Nagorno-Karabakh, a region of Azerbaijan long controlled by Armenia. After two months of military confrontations, a tripartite ceasefire was concluded, drastically altering the pre-existing territorial status quo.

The "Second Nagorno-Karabakh War" brings to light a fundamental question for international law on the use of force—and one that has received limited attention in legal doctrine. The question is this: when part of a State’s territory is occupied by another State for an extended period of time, can the former still invoke the right of self-defense to justify …

Legally Sliding Into War, Rebecca Ingber

Online Publications

Here we are again. Another presidential administration, another airstrike against another organized armed group against whom Congress has never authorized force, justified by self-defense, officially said to be necessary in light of some unstated, unspecified future threat.

Developing International Guidelines For Protecting Schools And Universities From Military Use During Armed Conflict, Steven Haines

International Law Studies

One consequence of armed conflict, especially that of a non-international character, is serious damage done to vital societal infrastructure. Education–schools and universities–can be severely disrupted, even subject to attack. Targeting of schools may not invariably be unlawful if educational facilities are being put to military use. Such use may itself not be unlawful but it can result in schools being transformed from civilian objects into military objectives–and subject, therefore, to lawful targeting. This was a problem highlighted by humanitarian NGOs a decade ago and led to the formation, by both NGOs and United Nations agencies, of the Global Coalition to …

Legal Reviews Of War Algorithms, Tobias Vestner, Altea Rossi

International Law Studies

States and scholars recognize legal reviews of weapons, means or methods of warfare as an essential tool to ensure the legality of military applications of artificial intelligence (AI). Yet, are existing practices fit for this task? This article identifies necessary adaptations to current practices. For AI-enabled systems that are used in relation to targeting, legal reviews need to assess the systems’ compliance with additional rules of international law, in particular targeting law under international humanitarian law (IHL). This article discusses the procedural ramifications thereof. The article further finds that AI systems’ predictability problem needs to be addressed by the technical …

Command Accountability For Ai Weapon Systems In The Law Of Armed Conflict, James Kraska

International Law Studies

The use of artificial intelligence (AI) in weapon systems enhances the ability of operational forces to fuse multispectral sensors to understand the warfighting environment, positively identify, track, and select targets, and engage them with the most appropriate effects. The potential for AI to help close the “kill chain” has raised concern that this creates a gap in accountability between the decisions of humans and the acts of machines, with humans no longer accountable for decisions made during armed conflict. This study suggests that there is no gap because the military commander is always directly and individually accountable for the employment …

Israel’S Perspective On Key Legal And Practical Issues Concerning The Application Of International Law To Cyber Operations, Roy Schöndorf

International Law Studies

The speech given by the Israeli Deputy Attorney General (International Law) at the Naval War College’s event on “Disruptive Technologies and International Law” sets out, for the first time, Israel’s position on the application of international law to cyber operations. Consistent with the position taken by the vast majority of States thus far, Israel considers that international law applies to such operations. The speech stresses that questions pertaining to the identification and application of relevant legal rules remain, given the profound differences between the cyber domain and traditional domains of warfare—land, sea, and air. Therefore, in Israel’s view, a cautious …