Collective Self-Defence in International Law Cambridge Studies in International and Comparative Law Series

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.

Introduction; 1. Delineating collective self-defence; 2. The history and development of collective Self-defence; 3. The requirements shared by individual and collective self-defence; 4. The purported declaration and request requirements for collective self-defence; 5. The issuer of a collective self-defence request; 6. The manner and form of a collective self-defence request; 7. Collective self-defence treaty arrangements; 8. The relationship between collective self-defence and military assistance on request; Conclusion; Bibliography.

James A. Green is the author of The Persistent Objector Rule in International Law (2016), which won the ESIL Book Prize, and The International Court of Justice and Self-Defence in International Law (2010), which won ASIL's Lieber Prize. He is the Co-Editor-in-Chief of the Journal on the Use of Force and International Law and co-rapporteur of the ILA's Use of Force Committee.