Sivakumaran's book The Law of Non-International Armed Conflict aims to ascertain the content of the substantial body of law applicable to non-international armed conflicts (NIAC), the scope of its application, and its methods of enforcement ‘while subjecting it all to critical analysis’ (p. 5). The book takes issue with the prevailing methodological approach by which this law has developed, which was primarily to draw on the law of international armed conflict (IAC). Underlying this approach was the idea that ‘the law of international armed conflict should be the standard to which the law of non-international armed conflict aspires’ (italics in original) (p. 2). In addition, resort was made to other fields of international law, such as international criminal law and international human rights law, for the purpose of the regulation of NIAC (p. 2). According to the author, however, these approaches carry the risk of directly transposing certain norms from one body to another without sufficient attention being paid to the ‘specificities’ of NIAC (p. 3).Footnote ¹ Unlike in IAC, at least one of the parties involved in NIAC is a non-state actor, and, while this fact has a certain impact on the operation of the law of NIAC, its consequences have been largely overlooked due to the predominant state-centrism in international law (p. 3). Therefore, the book's additional objective is to incorporate the perspectives of armed groups in the analysis of the content of the law of NIAC (p. 5). For this purpose, Sivakumaran investigates the positions of a number of armed groups including FARC (Columbia), RUF (Sierra Leone), PKK (Turkey), LTTE (Sri Lanka), CPN-M (Nepal), MILF (Philippines), and MLC (DRC). The author divides his study into three parts.

Part I discusses how international law has regulated NIAC (Chapters 1–4). Based on an overview of the history of the regulation of NIAC from the nineteenth century to the present, in Chapters 1, 2, and 3, the author argues that a dramatic change has occurred since the mid-1990s: judicial bodies, especially the ICTY, transformed the law of NIAC by modelling it on the law of IAC, with recourse to international criminal law and international human rights law. However, he finds ‘methodological difficulties’ (p. 65) or ‘methodological concerns’ (p. 78) in these approaches because they are likely to disregard the differences between these branches of law: the primary distinction between IAC and NIAC lies in the actors involved; international criminal law regulates war crimes that are serious violations of international humanitarian law. While the principle of the equality of obligations of belligerents applies in international humanitarian law, it does not apply in international human rights law. This explains why it is necessary to ‘translate’ certain norms when moving from one body of law to another (pp. 99–100).

Based upon this understanding, in Chapter 4, Sivakumaran outlines his original idea to take into consideration the involvement of armed groups in NIAC. Sub-section 3 of this chapter, ‘The less traditional “sources”’, points out that the ad hoc commitments of armed groups, for example unilateral declarations, bilateral agreements, and internal regulations, need to be referred to as one of the sources of the law of NIAC in light of their potential importance. The author suggests that while their normative status remains ‘unsettled’ (pp. 109–10), they may serve as ‘an interpretational tool’ for the law of NIAC because they are ‘useful for providing a sense of what has proven acceptable and in which areas there is contestation’ (p. 110). In order to ‘illustrate acceptance or violation of a particular rule’ (p. 112), a vast number of documents concerning these commitments are mentioned in Part II, which comprehensively examines the substantive law of NIAC (Chapters 5–11).

Chapters 5, 6, and 7 discuss issues surrounding the application of the law of NIAC. In this reviewer's view, given that the author's main arguments underline the involvement of armed groups in NIAC, the following observations in these Chapters particularly corroborate them: first, the grounds for the organization of armed groups is primarily to ensure their ability to comply with the law of NIAC (pp. 176–80), which ultimately makes the requirement of territorial control in Additional Protocol (AP) II less important (pp. 185–87).Footnote ² Second, transnational armed conflicts are a subset of the category of NIAC in view of the recognition that what distinguishes NIAC from IAC is not the location of the conflict, but the identity of the party to the conflict, consequently triggering the application of not only common Article 3 of the Geneva Conventions but also AP II (pp. 228–34).Footnote ³ Third, the geographical scope of the application of the law of NIAC depends on the location of the persons affected by the conflict rather than the location in which the conflict occurs (pp. 250–52).Footnote ⁴

The question to be addressed, then, is: which rules apply to NIAC? Chapters 8 and 9 discuss the so-called ‘law of Geneva’ and ‘law of the Hague’ respectively, suggesting that a substantial body of law regarding NIAC exists in both fields under customary international law. However, they point out that sufficient attention should be paid to the involvement of armed groups in NIAC in relation to certain rules: first, because conditions of detention are contingent on the capabilities of the parties to conflicts (Article 5(2) of AP II), armed groups are not required to provide state-of-the-art detention facilities (pp. 292–300). Second, given that due process guarantees (Article 6 of AP II) also depend on the capacities of the parties to conflicts, the content of such guarantees varies accordingly (pp. 305–10). Third, the military wings of armed groups could be attacked at any time because of their membership. According to the author, membership ought to be decided on the basis of two elements: the law of armed groups and ongoing direct participation in hostilities (pp. 359–62).

In a similar vein, the involvement of armed groups in NIAC should be considered in relation to the implementation and enforcement of the law, as examined in Chapters 10 and 11. The author judges mechanisms for the implementation and enforcement of the law of NIAC to be weak: the effectiveness of belligerent reprisals is called into question due to the possibility of abuse (p. 456) and the usefulness of third party mechanisms, especially protecting powers and fact-finding, is limited because they are created primarily for IAC situations (p. 473). Furthermore, apart from international and domestic prosecutions of war crimes, enforcement by human rights bodies is restricted in scope because they only have jurisdiction over individual states (p. 510). Considering the inadequacies of these systems, the author emphasizes the importance of internal measures of armed groups. He expects that dissemination, instruction, legal advice, and codes of conduct will allow the internalization of the relevant norms within armed groups (p. 440) and consequently aid the level of compliance with the law of NIAC.

Finally, Part III offers ways forward, especially for compliance. Chapter 12 examines the significant problem that armed groups have little incentive to comply with the law of NIAC because it does not provide for combatant immunity. Although some cases suggest that states have granted amnesty, which has an equivalent effect to immunity (pp. 519–520), to armed groups, the author explores the possibility for the engagement with armed groups on the law of NIAC within an overarching framework, by means of a legal agreement between states and armed groups. He sees it as indispensable for armed groups to get involved in the actual process of this framework's formulation because this would enable them to create and possess ‘a sense of ownership’ over the norms and thereby increase compliance (pp. 562–64). In addition, this instrument should bring together all relevant rules of international law and contain provisions on implementation and enforcement including dissemination, self-reporting, and external monitoring (p. 566).

While the author's approach of taking into account the perspectives of armed groups on the law of NIAC is empirically rich, insightful, and thought-provoking, he should also have tackled and investigated in depth some significant issues from a more theoretical point of view.

First and foremost, the reviewer cannot ascertain how one would be able to utilize the practices of armed groups as a matter of law to reveal the substance of the law of NIAC. The author does not fully examine this issue in Chapter 4 before reporting his empirical research in great detail. Certainly, in this respect, he points out that the ad hoc commitments of armed groups have ‘unsettled’ or ‘uncertain’ status in determining the existence of customary international law (pp. 109–10), and thus are not used ‘to determine whether or not the rule is one of customary international law’ (p. 112). However, at the same time, he considers they provide ‘a far better sense of the state of the law’ (p. 110) and are helpful ‘for informing the interpretation of particular rules’ (italics added) (p. 112). In relation to some rules, such as the principle of proportionality (p. 349) and precautions (pp. 351–57), he seems to refer not only to the practices of states, but also to the ad hoc commitments of armed groups, in determining their application to NIAC and their specific contents in customary international law. The reviewer cannot help but wonder whether these ad hoc commitments are supposed to entail a specific legal meaning which aids the further clarification of the law of NIAC, and if so, to what extent.Footnote ⁵

Furthermore, the reviewer certainly shares the author's concern about the extrapolation of other branches of law, especially the law of IAC, to the legal system of NIAC. Nevertheless, the reviewer is not necessarily satisfied with the author's analysis of the substantive law of NIAC in Chapters 8 and 9. The primary reason for this reservation is that the author seems to jump to conclusions on the convergence of law between IAC and NIAC without sufficiently examining some controversial points.

This critique holds true especially for the legal basis of detention, and the legal categories of armed groups under the law of targeting. The author's position on the legal basis of detention is extremely vague, but seems not to exclude the possibility of resort to the law of IAC, drawing on Articles 42 and 78 of the Fourth Geneva Convention (pp. 301–2). Although he cautions that each different situation in which detention takes place should be considered independently (pp. 302–3), he does not answer the most important question: why is such a resort possible?Footnote ⁶ In relation to the legal categories of armed groups under the law of targeting, the author identifies the membership approach as an appropriate one, and insists that the membership of armed groups should depend on fixed criteria including those set out in the law of armed groups. This would mean that the standard in the law of NIAC should be the same as that in the law of IAC. However, he does not explicitly spell out the reasons for this position, although he criticizes the stance taken in the ICRC Interpretive Guidance on the Notion of Direct Participation in Hostilities as being too narrow (pp. 361–62).Footnote ⁷

In addition, the author concludes that the law of NIAC is ‘not dissimilar’ to that of IAC (p. 568) with the exception of the law relating to the protection of civilians and persons hors de combat in particular (p. 69). Although the reviewer does not disagree with this conclusion, in order to reach it, the author rather uncritically relies on the findings of the ICRC Study on Customary International Humanitarian Law. His evaluation of the study underlies this approach: ‘the findings of the study will reverse the presumption as to the existence of a customary norm’ (p. 104). In other words, the burden of proof lies with those who argue that such a customary rule does not exist, because ‘the fact that the study identifies the existence of a particular customary norm serves to satisfy this burden’ (p. 104). However, this evaluation amounts to an overestimation in light of the criticisms faced by the approaches of the study to determine customary international law.Footnote ⁸ More importantly, given that the author's main concern is directed towards the extrapolation of law from IAC to NIAC, he should have more critically examined the study's findings because they are implicitly based upon the law of IAC as he recognized himself (pp. 58–59).

Because the author regards drawing extensively on the law of IAC as being fraught with ‘methodological difficulties’, it seems to the reviewer that the methods he employs to reach his conclusions in Chapters 8 and 9 do not necessarily correspond to his original concerns as expressed in the Introduction and Chapter 3.

A final remark relates to the issue of compliance. With respect to the causal relationship between the issuance of ad hoc commitments of armed groups and the level of compliance, the author suggests that the such issuance can be ‘a first step towards compliance’ and lead to ‘an increased compliance’ (p. 113). While his empirical research on compliance is very thorough, he should have tried to clarify the concept of compliance in international law. International legal scholars have engaged in acute debate on this topic, and various (sometimes competing) understandings have been presented.Footnote ⁹ It is therefore regrettable that although a great number of cases concerning compliance are considered throughout the book, there is hardly any reference to the author's understanding of the concept of compliance in Chapters 4 and 12.

These criticisms notwithstanding, the author expands our horizon with this book and has delivered a monumental masterpiece. The book won the American Society of International Law Francis Lieber Prize 2013, the ICRC Paul Reuter Prize 2013, and the European Society of International Law Book Prize 2014 for the most outstanding work of the year. The reviewer is of the opinion that this book is likely to be cited as one of the greatest academic achievements in this field.Footnote ¹⁰