Necessity is a notoriously dangerous and slippery concept-dangerous because it contemplates virtually unrestrained killing in warfare and slippery when used in conflicting ways in different areas of international law. Jens David Ohlin and Larry May untangle these confusing strands and perform a descriptive mapping of the ways that necessity operates in legal and philosophical arguments in jus ad bellum, jus in bello, human rights, and criminal law. Although the term "necessity" is ever-present in discussions regarding the law and ethics of killing, its meaning changes subtly depending on the context. It is sometimes an exception, at other times a constraint on government action, and most frequently a broad license in war that countenances the wholesale killing of enemy soldiers in battle. Is this legal status quo in war morally acceptable? Ohlin and May offer a normative and philosophical critique of international law's prevailing notion of jus in bello necessity and suggest ways that killing in warfare could be made more humane-not just against civilians but soldiers as well. Along the way, the authors apply their analysis to modern asymmetric conflicts with non-state actors and the military techniques most likely to be used against them. Presenting a rich tapestry of arguments from both contemporary and historical Just War theory, Necessity in International Law is the first full-length study of necessity as a legal and philosophical concept in international affairs.

AcknowledgmentsIntroductionI. Three Kinds of Necessity: Exception, License, and ConstraintII. A RoadmapIII. Normative PrescriptionsPart A. Necessity & Jus Ad BellumCh. 1. Necessity and the Principle of Last Resort in Just War TheoryI. Defining Aggression in the Just War TraditionII. Gentili and the Justification of Offensive WarIII. Grotius on Fear of AttackIV. The Grotian Principles of Last Resort and Ad Bellum NecessityV. Last Resort as the Ultimate RestraintVI. Equally Efficacious MeansCh. 2. Necessity and the Use of Force in International LawI. Necessity and Customary Treaty LawII. Necessity in Investor-State RelationsIII. Necessity in Jus ad Bellum ViolationsIV. Necessity as a Component of Self-DefenseV. ConclusionPart B. Necessity & Jus in BelloCh. 3. Necessity and Discrimination in Just War TheoryI. Necessity and Discrimination in Early Modern Just War TheoryII. Necessity and Humane TreatmentIII. Luck and NecessityIV. Military Necessity as a Form of Practical NecessityV. Relating Jus In Bello Proportionality and NecessityCh. 4. The Foundations of Necessity in IHLI. The ICRC and NecessityII. Lieber's Conception of NecessityIII. Necessity in the Nuremberg TribunalsIV. What's Right and What's Wrong with Lieber's NecessityV. ConclusionCh. 5. Necessity in Human Rights Law and IHLI. Human Rights NecessityII. Combining Human Rights Necessity with IHL NecessityIII. ConclusionsCh. 6. Necessity in Criminal LawI. Necessity in Domestic Criminal LawI. No Constraints on the Necessity DefenseIII. Ad Hoc ConstraintsIV. Principled ConstraintsV. ConclusionCh. 7. Striking a Balance Between Humanity and NecessityI. HumanityII. Humanitarianism and Human DignityIII. Humane TreatmentIV. Dignity and VulnerabilityV. Humanitarian RightsVI. Concluding Thoughts on the Principles of Humanity and NecessityPart C. Applying Necessity to Contemporary ConflictsCh. 8. Combatants and Civilians in Asymmetric WarsI. Pirates and Insurgents at WarII. Grotius on Non-State Actors in WarIII. Jus Ad Bellum IssuesIV. Jus In Bello IssuesV. Civil Wars and CiviliansCh. 9. Disabling vs. Killing in WarI. Specific Prohibitions versus General DutiesII. The Hors de Combat ArgumentIII. Least Harmful Means Test at the Geneva NegotiationsIV. Should Jus in Bello Require Disabling before Killing?VI. Necessity and Killing Fleeing SoldiersCh. 10. The Duty to CaptureI. Is Capture Required by Jus in Bello Necessity?II. Are Different Rules for Civilians and Combatants Morally Legitimate?III. Capture as a Requirement of Constitutional NecessityIV. The Moral Arguments for a Duty to CaptureCh. 11. Force ProtectionI. Understanding Force ProtectionII. Jus ad Bellum Necessity and Force ProtectionIII. Jus in Bello Necessity and Force ProtectionIV. The Hannibal ProcedureV. Reasonable Force ProtectionConclusionIndex