Chapter 4 looks at the concept of combatants and non-combatants, and its connected status, that of prisoner of war (POW). It examines who is entitled under IHL to combatant status, and examines those persons who have been denied combatant and POW status under IHL. Particular attention is paid to the status of resistance fighters, national liberation and guerrilla fighters, those participating in a levée en masse, and participants in non-international armed conflicts. The chapter outlines those categories of participant not entitled to combatant status such as spies, mercenaries, so-called unlawful combatants, and private military and security contractors. Chapter 4 also explores the current legal thinking regarding a contentious area of the law – that of civilians taking direct part in hostilities. The rules regarding POW status and the treatment of POWs are described. The chapter concludes by examining another developing area of the law: the power of detention in non-international armed conflicts.

The chapter discusses the application of the principle of distinction to combatants and civilians, the consequences of that distinction and the issue of those civilians who directly participate in hostilities both in IACs and NIACs. It then discusses the application of the concept in cyber warfare. The chapter then considers the positions of members of private military security companies, unlawful combatants and UN peacekeepers.

Chapter 21 addresses military commissions. Their history and evolution are described. During the Mexican-American War, they were a modest military law stopgap in foreign countries. The US Civil War and the Lieber Code (Chapter 2) made them what they are today: rough-edged military field tribunals to address the war crimes of foreign combatants. Their value was proved following World War II, when all the Allied states employed them. Guantánamo’s post-9/11 perverted version of military commissions, in the shadow of CIA black sites and “enhanced interrogations,” may have ended their utility: initiated by civilian political appointees with the aim of denying prisoners not just POW status but basic human rights and legal protections, Guantánamo’s military commissions have been an abject failure, brought to heel by civilian courts’ legal resistance and forced recognition of civilian legal oversight. Guantánamo’s record of eight convictions in eighteen years, three of which have been vacated, is proof of their legal ineffectiveness and moral hollowness.