Cavari, Efrat, & Yair: Contemplating Conquest: Public Opinion on the Forcible Seizure of Territory

Amnon Cavari (Reichman Univ.), Asif Efrat (Reichman Univ.), & Omer Yair (Reichman Univ.) have posted Contemplating Conquest: Public Opinion on the Forcible Seizure of Territory (PS: Political Science & Politics, forthcoming). Here's the abstract:

The norm against conquest—a central tenet of the international order—is eroding. This study is among the first to examine public support for this norm, using a real-world case: Israel’s seizure of Syrian territory following the collapse of the Assad regime in December 2024. Our survey experiment in Israel reveals that citizens are sensitive to the prohibition on conquest. They demonstrate greater support for an occupation that involves only military control of the forcibly seized territory and weaker support for civilian settlement in or annexation of the foreign territory: policies that amount to conquest. Our finding—a stronger preference for legally acceptable occupation over illegal settlement or annexation—sends a positive signal for the constraining power of norms.

Rosen: Perpetual War and International Law: Enduring Legacies of the War on Terror

Brianna Rosen (Oxford Programme for Cyber and Technology Policy) has published Perpetual War and International Law: Enduring Legacies of the War on Terror (Oxford Univ. Press 2026). Here's the abstract:

Nearly a quarter century after the September 11, 2001 attacks, the U.S.-led war on terror remains a defining force shaping international law, human rights, and global security. While major combat operations in Afghanistan and Iraq have formally ended, the long-anticipated shift from a war paradigm to a law enforcement approach has yet to materialize. Instead, U.S. and allied counterterrorism activities persist worldwide, raising urgent questions about the role of law in enabling and sustaining armed conflict.

Perpetual War and International Law brings together leading experts to confront the enduring legacies of the post-9/11 era and explore viable alternatives to the use of force. The volume traces how legal and policy frameworks have served to legitimize military action, eroding the boundary between war and peace. Contributors challenge prevailing interpretations of international law in an age of endless war and unconventional threats.

Drawing on insights from law, ethics, and security studies, the volume critically examines how legal and normative precedents established during the war on terror continue to shape contemporary conflicts. It offers bold pathways for shifting from a global order rooted in force to one grounded in restraint and the rule of law. Perpetual War and International Law is a vital intervention, inviting readers to reimagine how international law can constrain violence in an increasingly conflict-ridden world.

Klein, Purcell, & McNally: Submarines in International Law

Natalie Klein (Univ. of New South Wales - Law), Kate Purcell (Univ. of New South Wales - Law), & Jack McNally (Univ. of New South Wales - Law) have published Submarines in International Law (Cambridge Univ. Press 2026). Here's the abstract:

Submarines in International Law is the first book to explore both the legal history and the contemporary regulation of submarine operations in varied areas of international law. The analysis demonstrates the instances where submarines influenced the development of the law of the sea and the law of armed conflict, as well as highlighting where international law needs to give greater account for submarines in existing bodies of law-including international marine environmental law, the law on the use of force, navigational safety rules, transnational criminal law and international cultural heritage law. Submarine operations range from military and defence uses, to supporting research and commercial seabed industries, to ocean tourism and smuggling of illicit goods. International law regulates all these activities to varying degrees. While submarines may strive to be evasive objects in the ocean, this book demonstrates why they cannot and should not elude the reach of international law.

Call for Papers: The Use of Force in Recent Conflicts

The Canadian Yearbook of International Law has issued a call for papers for a Young Scholars’ Workshop on “The Use of Force in Recent Conflicts,” to be held at the University of Ottawa in the fall of 2026 on the margins of the Annual Conference of the Canadian Council on International Law. At the workshop, the selected authors will receive constructive feedback from senior scholars and practitioners. Subsequently, authors will submit their articles for consideration by the Canadian Yearbook of International Law, subject to peer review. The call is here.

Marxsen: Shades of Illegality in the Law Against War

Christian Marxsen (Humboldt-Universität zu Berlin) has published Shades of Illegality in the Law Against War (Oxford Univ. Press 2026). Here's the abstract:

The prohibition of force is a cornerstone of the international legal order. Yet, frequent violations raise pressing questions about the resilience of the law. This monograph investigates the complex realities behind these breaches in international law, to facilitate a deeper understanding of how disputes over norms governing the prohibition of the use of force shape-and sometimes strain-the legal order.

Introducing the concept of “shades of illegality,” this book develops a typology of illegality that distinguishes between the different forms of illegality and their specific effects on international legal norms and the international legal order in general. These six types of illegality include contested applications of agreed law, emergency-driven violations, and deliberate challenges aimed at reshaping legal norms. By unpacking these categories, the book reveals how different types of illegality exert varied effects on the stability and evolution of international legal frameworks.

Shades of Illegality in the Law Against War argues that conflicts over the application and interpretation, formulation, and further development of the law are not pathological, and that illegality can even play a constructive role in the overall functioning of the international order. However, it also warns of the corrosive impact of systemic opposition-where states seek to dismantle core legal principles such as jus contra bellum. Providing nuanced analysis from both a doctrinal and theoretical perspective, this book equips readers with the conceptual tools needed to clarify the role of illegality in the international order and to critically assess the state of the prohibition of force in international law.

Swaine: Prohibiting Threats of Aggression

Edward T. Swaine (George Washington Univ. - Law) has posted Prohibiting Threats of Aggression. Here's the abstract:

Recent events, particularly Russia’s invasion of Ukraine, have revived worries about the international regime regulating the use of force. Vastly less attention has been paid to what often precedes such attacks—threats to use force—and the prohibition on them. While the UN Charter and other legal instruments integrate the threats regime with the regime on actual uses of force, the two regimes are increasingly decoupled, in part because only one considers gradations: the use-of-force regime now identifies more serious variants like aggression and crimes of aggression; threats rules, by contrast, do not. This decoupling reflects real differences in the underlying wrongs, but it is also due to bureaucratic history and path dependence, including reluctance to criminalize threats of aggression while the underlying concept of aggression was still being developed.

As a result, international law and its institutions fail clearly to treat more serious threats, like threats to annex another state’s territory, as graver state conduct—putting aside, that is, whether criminalization is appropriate. This artificially limits the toolkit for addressing incipient aggression of the kind patently evident before Russia’s invasion of Ukraine. It has also impoverished consideration of potential aggression, such as may become inferable from U.S. policy concerning the Panama Canal and Greenland, before positions harden and avoidable consequences come to pass.

This Article proposes clearly defining and recognizing threats of aggression as prohibited state conduct. It evaluates the potential for deterring wrongdoing and proposes concrete and novel ways that institutions could develop and employ the rule. Such an initiative might discourage the most bellicose threats by states and even acts of aggression themselves.

Lieblich: The Death and Life of the Prohibition on Forcible Reprisals

Eliav Lieblich (Tel Aviv Univ. - Law) has posted The Death and Life of the Prohibition on Forcible Reprisals (Yale Journal of International Law, forthcoming). Here's the abstract:

That forcible reprisals between states are unlawful is taken for granted in contemporary international law. However, events in recent years have highlighted the resurgence of retaliatory force, challenging the foundational principles of the prohibition. This article seeks to uncover the normative assumptions underlying the prohibition on reprisals, demonstrate how these assumptions are challenged in the current international moment, and propose ways in which the prohibition can be revitalized.

In the pre-UN Charter era, forcible reprisals were considered lawful on the basis of three normative assumptions: that there was no "common judge" among sovereigns and thus self-help was justified; that self-defense and punishment were intertwined; and that international law was concerned with the rights of states rather than those of individuals. The UN Charter, in its prohibition on reprisals, sought precisely to counter these assumptions. However, as the article shows, international polarization and permissive doctrines on the use of force – in particular, those blurring the distinction between defense and punishment – have consistently eroded these foundations. The article exemplifies these erosive dynamics by focusing on the retaliatory cycle between Iran and Israel in 2024, situating it within the current moment of international polarization.

The article then proposes a normative framework to revitalize the prohibition. Chiefly, it offers a novel theoretical definition of reprisals as a form of opportunistic harm, one that cannot be justified even in the absence of a common judge. By doing so, the article acknowledges the fragmentation of the current global order while reaffirming the intrinsic wrong of reprisals even in turbulent international times.

Romani: Belligerent Reprisals from Enforcement to Reciprocity: A New Theory of Retaliation in Conflict

Francesco Romani (Geneva Academy of International Humanitarian Law and Human Rights) has published Belligerent Reprisals from Enforcement to Reciprocity: A New Theory of Retaliation in Conflict (Cambridge Univ. Press 2024). Here's the abstract:

This book challenges the traditional understanding of belligerent reprisals as a mechanism aimed at enforcing the laws of armed conflict. By re-instating reciprocity at the core of belligerent reprisals, it construes them as tools designed to re-calibrate the legal relationship between parties to armed conflict and pursue the belligerents' equality of rights and obligations in both a formal and a substantive sense. It combines an inquiry into the conceptual issues surrounding the notion of belligerent reprisals, with an analysis of State and international practice on their purpose and function. Encompassing international and non-international armed conflicts, it provides a first comprehensive account of the role of reprisals in governing legal interaction during wartime, and offers new grounds to address questions on their applicability, lawfulness, regulation, and desirability.

Conference: The Gaza War and International Law: Norms and Institutions

On December 17-18, 2024, the 19th Annual Minerva Conference on International Humanitarian Law will take place at the Hebrew University of Jerusalem. The theme is: "The Gaza War and International Law: Norms and Institutions." The program is here.

Yip: To Call a Spade a Spade: Use of Force Depriving a People of their Right to Self-Determination as Violation of Jus Contra Bellum

Ka Lok Yip (Hamad Bin Khalifa Univ.) has posted To Call a Spade a Spade: Use of Force Depriving a People of their Right to Self-Determination as Violation of Jus Contra Bellum (Journal on the Use of Force and International Law, forthcoming). Here's the abstract:

This article argues that a use of force which deprives a self-determination entity (‘SDE’) of its right to self-determination is prohibited under both Article 2(4) of the UN Charter and customary international law, even if there may not be sufficient practice accepted as law (opinio juris) to establish that such forcible deprivation of a SDE’s right to self-determination constitutes an armed attack that entitles the SDE to the right of self-defence. The obfuscation between a prohibited use of force and an armed attack triggering the right to self-defence often fans the escalation of conflict involving a SDE which claims the right to use force in self-defence (an issue discursively over-emphasized but not actually regulated under jus contra bellum) against the original use of force which deprives the SDE of its right to self-determination (an issue discursively under-emphasized but actually prohibited by jus contra bellum).

The article also argues that a State’s use of force to occupy or subjugate a SDE to permanently prevent an armed attack from emanating from that SDE does not qualify as lawful self-defence in the absence of an actual or imminent armed attack. Even when a State uses force in the name of self-defence against attacks emanating from a SDE, such use of force cannot satisfy the necessity requirement for lawful self-defence if the State could have taken non-forcible means to avert or stop the attack that emanates from the SDE, notably by relinquishing control over the SDE in discharge of its duty to respect the SDE’s right to self- determination. Where attacks by an armed group originating from a SDE involve serious violations of international humanitarian law (‘IHL’), an argument could be made that the attacks are simply unconcerned with the SDE’s right to self-determination, could not have been averted or stopped by the State relinquishing its control over the SDE and therefore render forcible self-defence necessary. While this argument cannot be precluded upfront, neither IHL provisions nor historical precedents suggest that IHL violations per se would sever the nexus between attacks by an armed group originating from a SDE and the pursuit of the SDE’s right to self-determination.

Pobjie: Prohibited Force: The Meaning of ‘Use of Force' in International Law

Erin Pobjie (Univ. of Essex - Law) has published Prohibited Force: The Meaning of ‘Use of Force' in International Law (Cambridge Univ. Press 2024). Here's the abstract:

Prohibited 'use of force' under article 2(4) of the UN Charter and customary international law has until now not been clearly defined, despite its central importance in the international legal order and for international peace and security. This book accordingly offers an original framework to identify prohibited uses of force, including those that use emerging technology or take place in newer military domains such as outer space. In doing so, Erin Pobjie explains the emergence of the customary prohibition of the use of force and its relationship with article 2(4) and identifies the elements of a prohibited 'use of force'. In a major contribution to the scholarship, the book proposes a framework that defines a 'use of force' in international law and applies this framework to illustrative case studies to demonstrate its usefulness as a tool for legal scholars, practitioners and students.

Green: Collective Self-Defence in International Law

James A. Green (Univ. of the West of England - Law) has published Collective Self-Defence in International Law (Cambridge Univ. Press 2024). Here's the abstract:

Collective self-defence can be defined as the use of military force by one or more states to aid another state that is an innocent victim of armed attack. However, it is a legal justification that is open to abuse and its exercise risks escalating conflict. Recent years have seen an unprecedented increase in the number of collective self-defence claims. It has been the main basis for US-led action in Syria (2014-) and was advanced by Russia in relation to its full-scale invasion of Ukraine (2022-). Yet there still has been little analysis of collective self-defence in international law. This book crucially progresses the debate on various fundamental and under-explored questions about the conceptual nature of collective self-defence and the requirements for its operation. Green provides the most detailed and extensive account of collective self-defence to date, at a time when it is being invoked more than ever before.

Fox: Invitations to Intervene After the Cold War: Toward a New Collective Model

Gregory H. Fox (Wayne State Univ. - Law) has posted Invitations to Intervene After the Cold War: Toward a New Collective Model (in Max Planck Trialogues on the Law of Peace and War, forthcoming). Here's the abstract:

The argument supporting a right to intervene at a government’s request would seem straightforward. The UN Charter endows states with a virtually absolute right to bar outside forces from entering upon their territory. But governments, as the state’s agent, have broad discretion to exercise this right or not to do so; and, if not, to invite foreigners to assist in any actions they could lawfully undertake themselves. That choice is simply an example of states’ general ability to consent to actions otherwise considered unlawful. Consent – so the argument goes – precludes the wrongfulness of the foreigners’ presence and vitiates any violation of the state’s territorial integrity.

Despite this appealing logic, few scholars believe the claim accurately describes contemporary international law. But there is even less agreement on the alternatives. This chapter will focus on two aspects of consensual interventions that recent scholarship has not addressed at length.

First, it asks whether any of the various theories of consent find support in a comprehensive assessment of post-Cold War practice. To my knowledge, no effort has been made to compile all examples of consensual intervention after the end of the Cold War and examine systematically how the United Nations, regional organizations and leading states have reacted. The discussion of this practice will rely on a new dataset compiled for this purpose.

Second, the chapter focuses particular attention on the practice of the UN Security Council. The data reveal that the Council has issued resolutions or Presidential Statements on an overwhelming proportion (82%) of consensual interventions since 1990. Many scholars have focused on the international community’s inability to agree on factual aspects of contested interventions. These include whether an invitation was in fact issued, whether the inviting party exercised effective control over a state and whether a conflict had reached the level of a ‘civil war’. But controversies over these factual predicates for a valid invitation are rendered largely irrelevant through collective determinations by the Council, which enjoys an authority to characterize legally significant facts and to distinguish between lawful and unlawful uses of force.

Wentker: Neutrality in International Legal Thought

Alexander Wentker (Max Planck Institute for Comparative Public Law and International Law) has posted Neutrality in International Legal Thought (in Research Handbook on International Legal Theory and War, Tom Dannenbaum & Eliav Lieblich eds., forthcoming). Here's the abstract:

This chapter discusses the key debates surrounding neutrality that international legal thought has had to grapple with. It shows how international legal thought has made sense of an institution that has been shaped by States’ pragmatic mindset in developing and invoking it. The chapter analyses how scholarship has positioned and continuously re-positioned neutrality within a dramatically changing international order in which neutrality has proved stubbornly resilient. In doing so, the chapter demonstrates that, however marginal neutrality’s relevance to current international law may appear at first sight, theoretical reflection on neutrality helps in better grasping the current international legal regulation of war as a whole, and even structural developments in general international law beyond war.

Brunk & Hakimi: The Prohibition of Annexations and the Foundations of Modern International Law

Ingrid (Wuerth) Brunk (Vanderbilt Univ. - Law) & Monica Hakimi (Columbia Univ. - Law) have posted The Prohibition of Annexations and the Foundations of Modern International Law (American Journal of International Law, forthcoming). Here's the abstract:

The international legal norm that prohibits forcible annexations of territory is foundational to modern international law. It lies at the core of three projects that have been central to the enterprise. The first focuses on settling title to territory as the basis for establishing state authority. The second regulates the use of force across (settled) territorial borders. The third provides for the people within each state’s (settled) borders collectively to determine their own fates. The norm that prohibits forcible annexations is integral to each of these projects independently, and by tying them together, has had a transformative effect on the legal system as a whole.

However, this prohibition is also misunderstood, both as a matter of history and in its relationship to other contemporary international legal norms. Because it is intertwined with all three of the above projects, its origins cannot be traced to only one or the other. The common narrative that describes it as the inevitable outgrowth of regulating war is, therefore, misleading and incomplete. That narrative overlooks the role that formerly colonized states played in securing this norm while seeking to establish themselves as states, through decolonization and claims of self-determination. In modern doctrine, too, the prohibition of annexations is often subsumed into the general prohibition on the use of force, when in fact, its normative influence extends much more broadly.

As a result, the norm’s significance and position in modern international law are consistently overlooked. Analysts have also, by and large, failed to appreciate that it is now caught up in a broader contest over the future world order and at risk of erosion. As deeply flawed as the previous world order was, jettisoning this norm is a dangerous path forward. From Ukraine to Palestine, Israel, the Nagorno-Karabakh region, the Golan Heights, Western Sahara, and the Chagos Archipelago, states and nonstate actors alike care deeply about exercising power over territory, which has historically been a primary impetus of interstate war.

Gill & Tibori-Szabó: The Use of Force and the International Legal System

Terry D. Gill (Univ. of Amsterdam - Law) & Kinga Tibori-Szabó (Univ. of Amsterdam - Role of Law in Armed Conflict and Military Operations research programme) have published The Use of Force and the International Legal System (Cambridge Univ. Press 2023). Here's the abstract:

This book provides in-depth coverage and analysis of the international law, rules and principles that govern the use of force. Through a unique intra-disciplinary perspective, it examines how the law on the use of force functions within the international legal system and how it interacts with other relevant areas of the law. This includes arms control law, the law governing the use of the international commons, the law of armed conflict and human rights law, and the law of international responsibility. It offers an accessible guide to the law on the use of force to students and practitioners, alongside providing a unique perspective on the place and function of the law on the use of force within the wider legal landscape which will appeal to both academic professionals and others interested in how law regulates the use of force.

Nußberger: Interstate Assistance to the Use of Force

Benjamin K. Nußberger has published Interstate Assistance to the Use of Force (Nomos 2023). Here's the abstract:

Unterstützung ist eine entscheidende Komponente zwischenstaatlicher Gewaltanwendung. Das Buch konturiert die völkerrechtliche Regulierung zwischenstaatlicher Unterstützungsleistungen zu internationaler Gewaltanwendung. Es zeichnet die einschlägige Praxis der Staaten in Resolutionen der Vereinten Nationen, in zwischenstaatlichen Verträgen und in mehr als 25 kriegerischen Konflikten – vom Korea-Krieg bis zum aktuellen Ukraine-Krieg – nach, ordnet sie historisch in die Entwicklung des Friedenssicherungsrechts ein, und setzt sie ins Verhältnis mit allgemeinen völkerrechtlichen Regelungen zur Beihilfe. Zugleich beleuchtet das Buch Unschärfen der bestehenden Regulierung und schafft so die Grundlagen für mehr Transparenz und expliziten Diskurs.

Whenever States use force in their international relations, interstate assistance is a vital component. The book clarifies the regulation of interstate assistance to a use of force under international law. It comprehensively reviews the relevant practice of States in United Nations resolutions, in international treaties and in more than 25 armed conflicts - from the Korean War to the current Ukraine war. It situates the regulation within the historic development of the ius contra bellum and contextualizes it with general rules of international law on complicity. Thereby, the book also sheds light on ambiguities of the regulation, thus providing the basis for more transparency and explicit discourse among both practitioners and scholars.

Schmitt & Biggerstaff: Aid and Assistance as a “Use of Force” Under the Jus Ad Bellum

Michael N. Schmitt (Univ. of Reading - Law) & W. Casey Biggerstaff (U.S. Naval War College) have published Aid and Assistance as a “Use of Force” Under the Jus Ad Bellum (International Law Studies, Vol. 100, 2023). Here's the abstract:

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 date, States have failed to meaningfully contend with the notion of indirect force, much less clarify its precise threshold. Accordingly, through the lens of the Russia-Ukraine conflict, this article examines whether, and if so, when a State's military aid or assistance that contributes to another State's use of force constitutes a separate and distinct use of force under international law. After concluding that aid or assistance can, under certain conditions, qualify as a use of force, the article proposes several non-exclusive factors that States are likely to consider when assessing whether aid or assistance from a supporting State crosses the prohibition’s threshold.

Symposium: The Legitimacy and Legality of War: From Philosophical Foundations to Emerging Problems

On April 14, 2023, the Saint Louis University School of Law will host a symposium on "The Legitimacy and Legality of War: From Philosophical Foundations to Emerging Problems." Details and registration are here.

Call for Papers: International Law and the Regulation of Resort to Force: Exhaustion, Destruction, Rebirth?

The Centre for International Humanitarian and Operational Law at the Faculty of Law of Palacký University, in collaboration with the Institute for International Law and International Relations at the Faculty of Law of the University of Graz, has issued a call for papers for a conference on "International Law and the Regulation of Resort to Force: Exhaustion, Destruction, Rebirth?" to take place on September 14-15, 2023, in Olomouc. The call is here.