A military response to global terrorism raises challenges to the existing moral and legal framework for conduct of war. Indeed, some might argue that the so-called war on terror requires adopting an altogether new framework for thinking about the conduct of war. The older framework, anchored in the 1949 Geneva Conventions, presupposes an antiquated model of war as a conflict between sovereign states, so the argument would go, and this traditional paradigm is irrelevant to the current challenge of fighting terrorist groups, which do not represent sovereign states, but which are nevertheless capable of armed attacks with a global reach. Such an argument would, however, exaggerate the case. Although the phenomenon of global terrorism does present new challenges to the ethics of war, these challenges can be handled by developing core just war principles and refining their application. In an effort to demonstrate this, at least in part, I will focus on the apparent challenge to the rule of distinction posed by the phenomenon of global terrorism.
 One significant set of ethical challenges raised by the fight against global terrorism can be considered a species of the general challenge posed to the rule of distinction by the phenomenon of irregular warfare. Irregular combatants are persons participating in hostilities without belonging to a regular armed force. Usually they fail to identify themselves clearly as combatants. The rule of distinction requires, however, that military forces distinguish between combatants and noncombatants. According to article 48 of Additional Protocol I to the 1949 Geneva Conventions, “the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives.”1 Irregular combatants, by virtue of the fact that they participate in hostilities, make themselves legitimate objects of attack. When irregulars do not identify themselves as combatants, however, those fighting against them have trouble distinguishing combatants from civilians. The dynamics of irregular warfare thus tend toward undermining the rule of distinction.
 Any attempt to bring distinction to bear on irregular warfare must therefore address at least two sets of questions. The first set of questions concerns targeting. What sort of conduct by civilians converts them into irregular combatants, thereby rendering them legitimate objects of attack? The second set of questions concerns legal status. Do irregulars participate in hostilities lawfully, and therefore enjoy the protections afforded lawful combatants by the laws of war (e.g., POW status if captured)? Or do irregulars participate in hostilities unlawfully, and are therefore guilty of criminal acts? These two sets of questions intersect at various points. Sorting through them will be easier if we consider the question of legal status first.
 Some of the debates surrounding the problem of global terrorism (e.g., arguments about the proper legal status and treatment of suspected terrorists when captured) are tied up with the issue of “lawful” and “unlawful” combatancy. All combatants are legitimate objects of attack, but different kinds of combatants are afforded different kinds of protections by the laws of war. Lawful combatants are those who participate in hostilities legitimately, while unlawful combatants participate in hostilities illegitimately. The lawful combatant enjoys what is called the “combatant’s privilege.”2 He has the right to participate in hostilities and therefore the right to kill. That right does not extend to everyone. A lawful combatant is permitted to do things a civilian without combatant’s privilege may not. Thus the combatant’s privilege also entails the protections afforded captured soldiers by the Third Geneva Convention (in particular, POW status). Captured soldiers are not treated as criminals. By contrast civilians who commit acts of war without the combatant’s privilege are not entitled to POW protection. Indeed, their participation in acts of war is criminal.3
 The proper way to determine the legal status of combatants in an armed conflict has been a matter of debate over the years. According to the international law of armed conflict as I understand it, the legal status of combatants can depend to a great extent on the status of the armed conflict. International law recognizes two different types of armed conflicts: (1) international conflicts between states, and (2) non-international conflicts between a state and a non-state actor, usually an internal, domestic party such as an insurgency. The distinction between these two types of conflict rests on the 1949 Geneva Conventions, specifically on the so-called common articles. Common article 2 reads, “the present Convention shall apply to all cases of declared war or of any other armed conflict which may arise between two or more of the High Contracting Parties, even if the state of war is not recognized between them.”4 In other words, a common article 2 conflict is one where two or more states are engaged in armed conflict. All four Geneva Conventions apply in article 2 conflicts. This situation contrasts with article 3 conflicts. Common article 3 enunciates a set of provisions that apply “in the case of armed conflict not of an international character occurring in the territory of one of the High Contracting Parties.”5 In other words, an article 3 conflict is between a state and an organized armed group within its own territory. In this case, the rest of the Geneva Conventions do not apply. Only article 3 applies in article 3 conflicts.
 In article 2 conflicts there is a clear path by which irregular combatants can acquire legitimacy. The Third Geneva Convention identifies the categories of persons who, if captured by the enemy, are entitled to POW protections. If a soldier is entitled to POW protections, then essentially he enjoys the benefits that come with lawful combatancy and the combatant’s privilege. Article 4.A.2 of the Third Geneva Convention lists four conditions irregulars must meet to qualify for POW status:
(1) that of being commanded by a person responsible for his subordinates; (2) that of having a fixed distinctive sign recognizable at a distance; (3) that of carrying arms openly; (4) that of conducting their operations in accordance with the laws and customs of war.6
These conditions apply, however, only in article 2 conflicts — not article 3 conflicts — and one might reasonably ask whether they were developed with the example of World War II era partisans in mind. Today one rarely, if ever, encounters irregular combatants in the context of article 2 conflicts. Irregulars are generally insurgents or terrorists not affiliated with a state party to a conflict. Most insurgency warfare occurs within the context of article 3 conflicts. Based on the 1949 Geneva Conventions, irregular combatants fighting in article 3 conflicts are not entitled to POW status under most conditions; they do not enjoy the combatant’s privilege, and they are not lawful combatants.
 The matter is complicated, however, by the fact that the laws of war are not comprised solely of the 1949 Geneva Conventions. Of particular relevance here is the 1977 Additional Protocol I to the 1949 Geneva Conventions. Although 175 states are party to this Protocol, the United States is not, because the United States objects to a number of the Protocol’s controversial provisions. First, article 1.4 of the Protocol seeks to apply the provisions of all four Geneva Conventions to article 3 conflicts in which “peoples are fighting against colonial domination and alien occupation and against racist regimes in the exercise of their right of self-determination.”7 In other words, article 1.4 applies the Geneva Conventions in their entirety not only to international conflicts, but also to non-international conflicts where insurgents profess to be fighting against colonialism, foreign occupation, and racism. This accords to irregular combatants a level of legitimacy not accorded by the Geneva Conventions themselves. Second, article 44.3 of Additional Protocol I significantly modifies the conditions irregulars must meet to qualify for POW status. This entails a modification of the terms of lawful combatancy. Instead of requiring irregulars to wear “a fixed distinctive sign recognizable at a distance,” article 44.3 requires only that irregulars “distinguish themselves from the civilian population while they are engaged in an attack or in a military operation preparatory to an attack.” Additionally, article 44.3, rather than requiring insurgents to carry their arms openly, requires only that they carry their arms “openly during military engagement.” Finally, article 44.4 stipulates that “A combatant who falls into the power of an adverse Party while failing to meet the requirements set forth [for irregulars] shall forfeit his right to be a prisoner of war, but he shall, nevertheless, be given protections equivalent in all respects to those accorded to prisoners of war by the Third Convention and by this Protocol.”8
 Although the United States initially signed Additional Protocol I, it has never ratified the treaty. President Ronald Reagan explained his decision not to forward the treaty to the Senate for ratification as follows:
Protocol I is fundamentally and irreconcilably flawed. It contains provisions that would undermine humanitarian law and endanger civilians in war. One of its provisions, for example, would automatically treat as an international conflict any so-called “war of national liberation.” Whether such wars are international or non-international should turn exclusively on objective reality, not on one’s view of the moral qualities of each conflict. To rest on such subjective distinctions based on a war’s alleged purposes would politicize humanitarian law and eliminate the distinction between international and non-international conflicts…. Another provision would grant combatant status to irregular forces even if they do not satisfy the traditional requirements to distinguish themselves from the civilian population and otherwise comply with the laws of war. This would endanger civilians among whom terrorists and other irregulars attempt to conceal themselves. These problems are so fundamental in character that they cannot be remedied through reservations, and I therefore have decided not to submit the Protocol to the Senate in any form.9
Given the broad international support that has developed for Additional Protocol I over the years, President Reagan’s judgment that the treaty was “fundamentally flawed” appears mistaken; however, the specific objections he raised to the legal innovations developed in article 1 and article 44 of the Protocol impress this author as sound. By loosening the requirement on irregular combatants to fight in the same manner required of regular combatants, the innovations in Protocol I serve to undermine the rule of distinction. Under this legal regimen — one not accepted by the United States — irregulars can enjoy all the protections that come with the combatant’s privilege by temporarily choosing to participate in hostilities, and at the same time enjoy all the protections afforded civilians by temporarily choosing not to participate in hostilities. Such a legal regimen can be easily abused. Irregulars with such protections have no incentive to distinguish themselves from civilians; yet, unless soldiers and civilians can be distinguished, the rule of distinction is meaningless.
 Those concerned with the ethics of war, both just war theorists and international lawyers, have a responsibility to develop a theoretical approach to insurgency warfare and to the phenomenon of global terrorism that preserves the principle of distinction. In fact, the last few years have witnessed steps in that direction. The American legal scholar Gary Solis has argued, for example, that a report on the concept of “direct participation in hostilities” adopted by the International Committee of the Red Cross in 2009 offers guidance for moving beyond some of legal disputes surrounding Additional Protocol I.10 Although the ICRC report does not address questions about the legal status of irregulars, it does contribute to our thinking about the proper way to distinguish between combatants and noncombatants. In this respect, the report helps to clarify, refine, and reinforce the rule of distinction in relation to irregular combatancy.
 The concept of “direct participation in hostilities” appears in Additional Protocol I, article 51.3, according to which: “Civilians shall enjoy the protection afforded by [the Additional Protocol], unless and for such time as they take a direct part in hostilities.”11 The concept thus applies to civilians and indicates the conditions under which civilians surrender their immunity from direct attack; namely, when they participate directly in hostilities. The conceptual challenge has been to define what “direct participation in hostilities” means. The 2009 ICRC report identifies three constitutive elements of direct participation in hostilities. First, “the act must be likely to adversely affect the military operations or military capacity of a party to an armed conflict.” The report refers to this as a “threshold of harm” criterion. Second, “there must be a direct causal link between the act and the harm likely to result” from the act. The report refers to this criterion as “direct causation.” Third, “the act must be specifically designed to directly cause the required threshold of harm in support of a party to the conflict.”12 The report refers to this as a “belligerent nexus.” Although much more could be said about each of these criteria, the crucial point is that they offer guidance for distinguishing between the kind of participation in hostilities which causes civilians to forfeit their immunity from direct attack and the kind of general civilian support for a party to the conflict that does not entail losing civilian protections. Local civilians may offer support and assistance to insurgents with whom they sympathize. That kind of support does not make them legitimate objects of direct attack. Only when civilians participate in acts directly intended to cause the required threshold of harm within a belligerent nexus do they forfeit their noncombatant immunity and become legitimate objects of attack.
 Importantly, the ICRC guidelines do not focus on the legal status of irregulars, but rather on the kind of activity that causes civilians to become legitimate objects of attack. Because the ICRC report offers functional criteria of combatancy, it might appear to be continuing the expansive legal protection of irregulars laid out in Additional Protocol I, article 44. Indeed, the ICRC report makes clear that the “notion of direct participation in hostilities refers to specific acts carried out by individuals as part of the conduct of hostilities between parties to an armed conflict.”13 This implies that civilians, and hence irregulars, lose their immunity from attack for only so long as they directly participate in hostilities. Once they cease direct participation in hostilities, they regain their civilian protections. Of course, they can still be tried for acts of war committed as unlawful combatants if they participated in hostilities without enjoying combatant’s privilege. So understood, the ICRC guidelines might appear to reiterate the problems identified by President Reagan at the time he rejected Additional Protocol I. Fortunately, the ICRC guidelines help to move us beyond President Reagan’s objections by introducing a new concept to clarify further the notion of direct participation in hostilities. This is the concept of “continuous combat function.”
 In non-international article 3 conflicts, certain individuals may assume a “continuous combat function” by virtue of their integration into the “organized armed group” of a non-state actor. Such individuals become legitimate objects of attack in a way analogous to members of the armed forces of a State party to a conflict. As the ICRC report explains:
Civilians lose protection against direct attack for the duration of each specific act amounting to direct participation in hostilities, whereas members of organized armed groups belonging to a non-State party to an armed conflict cease to be civilians … and lose protection against direct attack, for as long as they assume their continuous combat function.14
Continuous combat function is the criterion of membership in what the ICRC report calls an organized armed group. Organized armed groups represent the armed forces of non-State parties. By identifying organized armed groups, the ICRC report is attempting to apply the principle of distinction to non-international conflicts. According to the report:
It is crucial for the protection of the civilian population to distinguish a non-State party to a conflict (e.g., an insurgency, a rebellion, or a secessionist movement) from its armed forces (i.e., an organized armed group). As with State parties to armed conflicts, non-State parties comprise both fighting forces and supportive segments of the civilian population, such as political and humanitarian wings. The term organized armed group, however, refers exclusively to the armed or military wing of a non-State party: its armed forces in a functional sense. This distinction has important consequences for the determination of membership in an organized armed group as opposed to other forms of affiliation with, or support for, a non-State party to the conflict.15
Not every civilian who sympathizes with or supports a non-state party to a conflict is a legitimate object of attack. Only those persons who participate directly in particular hostile acts or who assume membership in the organized armed group of a non-state party fall into this category. The criterion of membership in an organized armed group is “whether a person assumes a continuous function for the group involving his or her direct participation in hostilities.”16 Nevertheless, continuous combat function is distinct from direct participation in hostilities. As the report states: “Individuals whose continuous function involves the preparation, execution, or command of acts or operations amounting to direct participation in hostilities are assuming a continuous combat function. An individual recruited, trained and equipped by such a group to continuously and directly participate in hostilities on its behalf can be considered to assume a continuous combat function even before he or she first carries out a hostile act.”17
 This concept of continuous combat function has clear implications for the way we consider military responses to global terrorism. Under the Obama Administration, for example, the United States has developed a focused strategy of targeted killing of al Qaida members, and that policy has sometimes been the object of moral criticism. The analysis in this paper suggests that the policy of targeted killing cannot be criticized on grounds that it violates the rule of distinction. Al Qaida is an organized armed group engaged in an article 3 conflict against the United States. Active and integrated members of al Qaida have a continuous combat function by virtue of which they are legitimate objects of military attack, even when they are not directly engaged in a hostile act. The intentional and targeted killing of al Qaida members is therefore inherently compatible with the laws of war. This is not to suggest there are never reasons to object to a particular case of targeted killing. Perhaps a particular attack will cause disproportionate collateral damage; perhaps some targeted individuals do not in fact possess a continuous combat function; perhaps the particular drone missile will be fired by a person who does not belong to the regular armed forces of the United States; perhaps the attack does not take into account adequately the sovereignty of a particular state, and so on. These sorts of objections, however, are to particular instances of targeted killing, rather than objections to the policy of targeting killing itself. Nothing about that policy appears inherently incompatible with the laws of war. Attending carefully and thoughtfully to the laws of war is something that not only proponents, but also critics of the so-called “war on terror” ought to do.
1. Adam Roberts and Richard Guelff, eds., Documents on the Laws of War (Oxford: Oxford University Press, 1989): 414.
2. On the “combatant’s privilege” see Gary D. Solis, The Law of Armed Conflict: International Humanitarian Law in War (Cambridge: Cambridge University Press, 2010): 41.
3. On lawful and unlawful combatancy, see Yoram Dinstein, The Conduct of Hostilities under the Law of International Armed Conflict (Cambridge: Cambridge University Press, 2010) (kindle edition): chapter 2.
4. Documents on the Laws of War: 171.
5. Ibid: 172.
6. Ibid: 218.
7. Ibid: 390.
8. Ibid: 412.
9. President Ronald Reagan, “Letter of Transmittal” January 29, 1987. Reproduced in Gary D. Solis, The Law of Armed Conflict: 144.
10. See, Gary D. Solis, The Law of Armed Conflict: 202–219.
11. Documents on the Laws of War: 415.
12. “Interpretive Guidance on the Notion of Direct Participation in Hostilities under International Humanitarian Law,” International Review of the Red Cross vol. 90, no. 872 (Dec. 2008): 995–6. The study can be accessed through website of the International Committee of the Red Cross.
13. Ibid: 995.
14. Ibid: 996.
15. Ibid: 1006.
16. Ibid: 1007.