Editors' note: This post appears as an entry in a series examining Dr Nathan Derejko's book, Identifying Non-International Armed Conflict published by Cambridge University Press. The series features alternating posts with our friends at Armed Groups and International Law. The series introduction can be found here.
Professor Nathan Derejko's book Identifying Non-International Armed Conflict (NIAC) is not only a timely reminder that this type of armed conflict remains prevalent today, but is also a thoughtful contribution to the scholarly literature on NIAC. This includes its treatment of the “Classification of Battlefield Actors During NIAC,†Chapter 3, which is one of the least settled areas of the law of non-international armed conflict.
The Parties
The factual premise is self-evident. NIAC can no longer be viewed or understood through the traditional paradigm of a State fighting a single insurgent organization. Contemporary NIACs “feature†a diverse array of organized non-State armed groups (NSAG), pro-government militias, foreign State interveners, and peace operations to name but a few, all of which may fight either alongside, through, or in parallel with existing belligerents. Derejko offers a framework for classifying battlefield actors built around three distinct concepts: a “party†to a NIAC; actors that “belong†to a party; and actors merely “supporting†a party. That framework, he argues, is not a taxonomy for its own sake. It is meant to answer practical legal questions: when can violence by multiple groups be aggregated for the purpose of conflict classification; how many NIACs may exist in a given theatre; which actors are bound by international humanitarian law (IHL), and to whom battlefield conduct should be attributed.
The chapter proceeds in three overlapping stages. First, Derejko clarifies the concept of a party to a NIAC, pointing out that it is broader than the armed forces that act on its behalf. A party may be a State, an organized non-State armed group, an international organization, a de facto regime, and even an organized criminal group, as long as it has demonstrated the ability to engage in a NIAC. The specific label attached to an NSAG, as he reminds us, does not matter. Second, he turns to “belonging,†a concept drawn from the law of international armed conflict and repurposed here to define the outer limits of a party to a NIAC. Third, he addresses “supporting,†which he treats as a distinct basis on which a new actor may become an additional party to a pre-existing NIAC without becoming part of the supported party's armed forces.
The first stage is important because Derejko avoids collapsing the legal identity of a party into any single armed formation. The distinction between a party and the armed forces of a party allows him to explain how one party may contain multiple components without every component becoming a distinct party to a distinct NIAC. He illustrates the point with examples that range from State institutions to organized armed groups with military, political, judicial, or administrative wings. The broader implication is that NIAC law does not impose rigid limits on the kinds of entities capable of becoming parties. What matters is not formal status, motive, or organizational designation, but the demonstrated capacity to engage in armed conflict. That is a useful reiteration of the factual premise according to which it may no longer be assumed that NIAC will always involve a territorial State and a single non-State armed opposition group.
“Belongingâ€
The crux of the chapter, however, lies in Derejko's treatment of “belonging.†He is explicit that this concept is not drawn from the rules governing NIAC, but transposed from the express and implied operation of the law of international armed conflict, i.e., the 1907 Hague Regulations, The Third (Prisoner of War) Geneva Convention of 1949, and Additional Protocol I of 1977. He argues that the concept is functionally necessary in NIAC. Without reliance on such a category, it becomes difficult to explain how multiple organized armed groups can act on behalf of one party or why one entity should be legally responsible for the conduct of another. In his view, a group that “belongs†to a party is operating, whether de jure or de facto, as part and parcel of that Party's armed forces. The relationship is defined by authority, control, and command.
This basic proposition is not entirely new. The jurisprudential point of departure remains the International Criminal Tribunal for former Yugoslavia Appeals Chamber's (ICTY) judgment in Tadić, which acknowledged that the “content of the requirement of ‘belonging to a Party to the conflict' is far from clear or precise,†while linking it to a relationship of dependence, allegiance, and control (para. 93). The scholarly literature has long reflected the same uncertainty. Some writers referred to by Derejko, such as Katherine Del Mar, treated belonging as a relatively low-threshold notion satisfied by a de facto agreement that an irregular group would fight on a State's behalf. Others, including Keiichiro Okimoto, have been more skeptical of reducing the matter to a loose agreement or borrowing too heavily from State responsibility doctrine. (The International Committee of the Red Cross's (ICRC) 2020 Updated Commentary on GC III addresses the belonging issue as well but, curiously, Derejko does not engage with it.) Derejko's intervention should be read against that background. What makes it significant is not that he identifies the issue, but that he gives it sharper content.
His central claim, as already mentioned, is that what is inherent in belonging under IHL is a relationship of command and control. That proposition matters because it shifts the inquiry toward the operational structure of the relationship between an armed group and a party to the conflict. Derejko is not persuaded that shared objectives, allegiance, or even significant assistance are enough. Nor is he willing to situate belonging in the rules on attribution under the general norms on State responsibility. Instead, he argues that the relevant question is whether an organized non-State armed group is sufficiently integrated into a party's warfighting structure to be regarded as a part of its armed forces.
Command and Control
A key and original part of the chapter is the way in which Derejko elaborates on that standard. Drawing on military doctrine, he distinguishes between strategic, operational, and tactical command and control. Strategic control is too broad, because it would risk sweeping in every group that merely shares overarching aims or professes allegiance to the same cause. Tactical control is too narrow, because it would demand something like battlefield micromanagement and would miss the higher authority that plans and coordinates operations without directing each engagement. Derejko therefore locates the threshold at the operational level. In his view, a group belongs to a party when that party exercises a de jure or de facto level of authority and control functionally equivalent to operational command and control: sufficient to develop, authorize, or coordinate an armed group's military operations, without necessarily directing every tactical move.
This is the chapter's most discernible development of the existing literature on NIAC, albeit one that may lead to a new round of scholarly agreement, rebuttal, or requests for further clarification. The relevant jurisprudence has already established that some form of control matters. The literature has already debated whether belonging requires a de facto agreement, allegiance, or a firmer institutional relationship. Derejko gives the debate a more tangible focus. He offers a middle ground between two extremes: low-threshold theories that risk overinclusion; and attribution models derived from public international law that risk demanding too much. In practical terms, his test asks whether an organized non-State armed group is sufficiently integrated into a party's warfighting apparatus to be treated as one of its armed formations, without requiring that every act be attributable to the latter under the stricter standards of State responsibility. That approach, whether one agrees with it or not, may be said to mark a genuine development in scholarly reflection on the classification of actors in NIAC rather than being a restatement of previous debates.
Attribution
Derejko also addresses the relationship between belonging and attribution. He explains why the International Court of Justice's “effective control†test is too narrow for this purpose: it is conduct-specific, akin to tactical control, and would produce an unstable conception of belonging that appears and disappears with particular operations. He is more receptive to the ICTY's “overall control†test because it is relational rather than episodic, but criticizes it for failing to specify the level at which planning, organization, and coordination must occur. His own answer, again, is operational command and control. In that respect, the chapter shows that one need not choose between the bluntness of low-threshold belonging theories and the rigidity of general State responsibility doctrine. IHL interpretation can, and should serve to fill in conceptual gaps.
Support
The Chapter's second major strength lies in how carefully it separates belonging from support. Derejko treats support not as a diluted form of belonging, but as a distinct legal category with different consequences. If a new actor on the battlefield does not belong to an existing party and does not independently satisfy the Tadić test so as to generate a separate NIAC, the question becomes whether it is nonetheless supporting a party to a pre-existing NIAC. Here Derejko engages directly with the ICRC's support-based approach, under which intervening forces may become an additional, co-party to a pre-existing NIAC if there is a prior conflict, if they undertake acts related to the conduct of hostilities, if those acts support an existing party, and if that support follows an official decision to do so. (Derejko does not endorse the last condition.)
Again, the underlying debate is not new. Tristan Ferraro and the ICRC initially developed the support-based approach in relation to foreign intervention in NIAC. Derejko integrates it into a broader framework of classification and clarifies the distinction between belonging and support. Belonging makes an actor part of a party's armed forces. Support does not dissolve the supporter's distinct identity. It makes the supporter an additional party on the same side, not a subordinate component of the existing party. That distinction is analytically valuable because it explains how the same battlefield can contain multiple parties without multiplying conflicts, and why not every cooperative relationship should be treated as incorporation into a single belligerent entity.
Glosses
For all its conceptual insights, however, the chapter may be said to gloss over several important issues that might have been more fully explored. The first is evidence. Derejko's framework may be compelling in theory, but its utility will turn on proof. What kinds of facts are needed to establish operational command and control rather than mere coordination, sponsorship, or common purpose? Joint planning structures, joint operations, communications, compliance with ceasefires, territorial divisions of responsibility, weapons flows, personnel transfers, and financial dependence all seem relevant, but the chapter does not develop a sustained evidentiary methodology.
A second is the temporal aspect. Â Armed groups split, merge, defect, and realign. The framework would have benefited from more explicit discussion of when belonging begins, when it ends, and whether it can exist intermittently or only through sustained operational integration.
A third point concerns implications for targeting and detention. Derejko is careful to say that identifying belonging does not itself alter the substantive rules governing targeting and detention, which is correct. But the framework plainly affects who counts as part of a party's armed forces and therefore bears directly on status-based targeting, continuous combat function, and detention responsibilities. A more explicit discussion of those consequences would have enhanced the chapter's operational value.
Concluding Thoughts
Even with those reservations, Chapter 3 deserves careful attention. Its novelty does not lie in discovering an untouched concept. Belonging, co-belligerency, foreign support, and the problem of multiple armed actors have all been discussed before in both jurisprudence and scholarship. What Derejko offers is an internally coherent NIAC-specific framework that brings these ideas into relation with one another. He distinguishes party from armed forces, belonging from attribution, and support from belonging; he grounds belonging in command and control and gives the law of NIAC a clearer vocabulary for dealing with crowded battlefields. In a field where courts and commentators have often recognized the problem without quite solving it, that is a contribution to be welcomed.
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Jelena Pejic is the 2023 Annual Lieber Scholar and she was formerly a Senior Legal Adviser in the Legal Division of the ICRC in Geneva.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.Â
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Photo credit: AMISOM
