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. This title is also available as Open Access on Cambridge Core.

‘Erin Pobjie’s Prohibited Force is an extraordinary book. Its combination of theoretical sophistication and empirical rigor is both striking and rare. … I expect to return to [the early chapters] often. … I have learned so much from Pobjie’s outstanding book.’

Adil Ahmad Haque - Professor of Law and Judge Jon O. Newman Scholar at Rutgers Law School, author of Law and Morality at War (OUP, 2017)

‘For me, there is no question that Prohibited Force is the most detailed and sophisticated treatment of the meaning of ‘use of force’ conducted to date … It is a major addition to our toolkit for understanding what is, after all, a cornerstone rule of international law.’

James A. Green - Professor of Public International Law at the University of the West of England, Bristol, UK , co-rapporteur of the International Law Association’s Committee on the Use of Force and a former editor-in-chief of the Journal on the Use of Force and International Law. Author of Collective Self-Defence in International Law (CUP, 2024)

‘The book is a must-read for anyone working in the area. Erin Pobjie’s writing is clear and engaging. The book is carefully researched, thought-provoking, and deeply innovative.’

Alejandro Chetman - Dean and Professor of Law at Universidad Torcuato Di Tella

‘This expertly researched and argued text is already sure to prove invaluable for decision-makers at all levels.’

Andrew Clapham - Professor of International Law at the Geneva Graduate Institute and the author of War (OUP, 2021)