Lieber Studies Volume 5

Necessity and Proportionality in International Peace and Security Law

Edited by Claus Kreß and Robert Lawless

Edited Volume, 526 Pages
ISBN: 9780197537374
Published Oct. 5, 2020

Published by Oxford University Press


Disclaimer: Books in the Lieber Studies Series are not official publications of the United States Military Academy, Department of the Army, or Department of Defense. The views expressed in these volumes represent the authors’ personal views and do not necessarily reflect those of the Department of Defense, the United States Army, the United States Military Academy, or any other department or agency of the United States Government. The analysis presented stems from academic research of publicly available sources, not from protected operational information. 



Necessity and proportionality hold a firm place in the international law governing the use of force by states, as well as in the law of armed conflict. However, the precise contours of these two requirements are uncertain and controversial. The aim of Necessity and Proportionality in International Peace and Security Law is to explore how necessity and proportionality manifest themselves in the modern world under the law governing the use of force and the law of armed conflict, and how they relate to each other.

The book explores the ways in which necessity and proportionality are applied in practice and addresses pressing legal issues in the law on the use of force, including the controversial “unwilling and unable” test for the use of force in self-defense, drones and targeted killing, the application of this legal regime during civil war, and the need for further transparency in states’ justification for the use of force in self-defense.

The analysis of the role of military necessity within the law of armed conflict on the modern battlefield focuses on the history and nature of the principle of military necessity, the proper application of the principle of proportionality, how commanders should account for mental harm in calculating proportionality, and the role artificial intelligence and autonomous weapons systems may play in proportionality analysis. The book concludes with a discussion of the potential role of proportionality in the law governing post-conflict contexts.


Table of Contents

Brigadier General Joseph B. Berger III

Claus Kreß

PART ONE: An Encounter of International Law with Morality
1. Necessity and Proportionality in Morality and Law
Jeff McMahan

PART TWO: Considerations of Overarching Significance
2. On the Continuous and Concurrent Application of ad Bellum and in Bello Proportionality
Eliav Lieblich

PART THREE: The International Law Governing the Use of Force
3. The Essential Link Between Proportionality and Necessity in the Exercise of Self-Defense
Geoffrey S. Corn

4. The Unwilling and Unable Test for Extraterritorial Defensive Force: Why Force Is Permitted Against the Territorial State
Jens David Ohlin

5. Drones Programs, the Individualization of War, and the ad Bellum Principle of Proportionality
Rebecca Mignot-Mahdavi

6. The Quest for an Internal Jus ad Bellum: International Law’s Missing Link, Mere Distraction, or Pandora’s Box?
Tom Ruys

7. Article 51’s Reporting Requirement as a Space for Legal Argument and Factfulness
Larissa van den Herik

PART FOUR: The International Law of Armed Conflicts
8. Sequences in Military Necessity for the Jus in Bello
Dino Kritsiotis

9. Practical and Conceptual Challenges to Doctrinal Military Necessity
Robert Lawless

10. Considerations of Necessity Under Article 57(2)(a)(ii), (c), and (3) and Proportionality Under Article 51(5)(b) and Article 57(2)(b) of Additional Protocol I: Is There Room for an Integrated Approach?
Wolff Heintschel von Heinegg

11. Specifying the Proportionality Test and the Standard of Due Precaution: Problems of Prognostic Assessment in Determining the Meaning of “May be Expected” and “Anticipated”
Stefan Oeter

12. The Proportionality Rule and Mental Health Harm in War
Sarah Knuckey, Alex Moorehead, Audrey McCalley, and Adam Brown

13. Towards the Special Computer Law of Targeting
Masahiro Kurosaki

PART FIVE: Jus Post Bellum
14. The Duty to Pay Reparations for the Violation of the Prohibition of the Use of Force in International Relations and the Jus Post Bellum
Elisabeth Günnewig