The Conduct of Hostilities under the Law of International Armed Conflict: 4th Edition

by | Dec 5, 2022

Conduct of Hostilities 4th Ed.

The fourth edition of The Conduct of Hostilities under the Law of International Armed Conflict is a thoroughly revised and updated version of a book originally published in 2004 and revised twice before: in 2010 and in 2016. It examines in detail the jus in bello, which has not stood still since 2016. The text serves as a companion to three other volumes published by Cambridge University Press (dealing respectively with the jus ad bellum, the law of belligerent occupation, and non-international armed conflicts).

Currently, the jus in bello is facing an unprecedented crisis owing to vast civilian carnage and devastation flagrantly inflicted by a Permanent Member of the Security Council (Russia) in its international armed conflict with Ukraine. A serious discussion of the criminal dimensions of the indiscriminate attacks in Ukraine will have to await the termination of the war, when detailed evidence will hopefully be sifted and analyzed more dispassionately. But, independently of the perpetration of war crimes, the new edition mentions the Ukrainian hostilities in diverse connections ranging from the application of the jus in bello in a self-proclaimed “Special Military Operation” to the enrollment into service of foreign volunteers (and mercenaries).

The Ukrainian hostilities aside, the new edition raises a raft of new jus in bello questions against the background of recent international judicial decisions, developments in treaty law, and advances in customary law as interpreted in the very extensive doctrinal literature.

Recent Case Law

The jurisprudence of the International Criminal Court (ICC) is increasingly pertinent to the jus in bello. Two surprising judgments rendered by the Appeals Chamber should be flagged in particular. One is the 2018 Bemba decision, in which the Appeals Chamber (by 3:2 majority vote) reversed a lower instance conviction for war crimes of a Congolese Commander-in-Chief of an organized armed group fighting in the Central African Republic. Two of the majority Judges expressed the opinion that command responsibility is limited to (junior) unit commanders, since “[i]t is simply impossible for senior commanders to control hundreds or thousands of individual troops effectively,” and leading officers (not being physically proximate) “are entitled to rely on lower level commanders to keep their troops in check and to deal with deviant behaviour.” This approach is entirely incompatible with a long line of previous judicial precedents (starting with the seminal U.S. Supreme Court opinion in the Yamashita case) holding high-ranking commanders responsible for dereliction of duty in not suppressing unlawful conduct by remote subordinates. Bemba is an exceedingly controversial decision that will surely spark much debate in the years ahead.

Another unexpected decision is the 2019 Jordan Referral re Al-Bashir Judgment, where the Appeals Chamber pronounced that “there is neither State practice nor opinio juris that would support the existence of Head of State immunity under customary international law vis-à-vis an international court.” The case of Al-Bashir, a Head of State of Sudan indicted (when in office) following the Darfur atrocities, has generated prolific commentaries. Until the Jordan Referral, the matter was generally viewed through the lens of a Rome Statute’s provision regarding “diplomatic immunity of a person or property of a third State” (i.e. a State that is not a Contracting Party to the Statute), whereby it is necessary to “first obtain the cooperation of that third State for the waiver of the immunity.” It has commonly been assumed that Heads of States benefit from an immunity akin to that of diplomatic envoys. But in Jordan Referral the ICC Appeal Chamber bluntly stated that, as far as Heads of States are concerned, “no waiver is required as there is no immunity to be waived.” Admittedly, this unequivocal pronouncement has met with mixed response by scholars. Nevertheless (as the new edition points out), even if the Judgment has moved ahead of existing law, there is no doubt that it gives a strong push to the evolution of a new custom in that direction.

It might be added that, in the 2021 Ntaganda Judgment delivered by the ICC Appeals Chamber (in dealing with a non-international armed conflict), a crucial bone of contention was whether the classical definition of the term “attacks” (set forth in Article 49(1) of Additional Protocol I, which reflects customary jus in bello) – namely, “acts of violence against the adversary, whether in offence or in defence” – coincides with that of “attacks” alluded to in the context of war crimes in the Rome Statute. Yet, indisputably, the jus in bello definition of “attacks” remains intact; and in any event, the difference of opinions in Ntaganda has no impact upon non-Parties to the Rome Statute (like the United States). The contours of the definition of “attacks” are of immense import in many areas. Most conspicuously, “cyberattacks” do not qualify as “attacks” in the jus in bello sense unless entailing violence.

Recent Treaty Law

The general disinclination of States to attempt to formulate new treaties relating to methods of hostilities continues unabated. By contrast, no such reluctance is exhibited with respect to means of warfare. Indeed, in 2017, a revolutionary Treaty on the Prohibition of Nuclear Weapons (TPNW) was adopted by a diplomatic conference convened by the UN General Assembly.

This is a prominent instrument, but prominence is not to be confused with empirical significance. The new edition emphasizes that the TPNW cannot be considered as more than a symbolic gesture, inasmuch as it was concluded in the absence of – and in the face of trenchant opposition by – the nuclear-weapon States and other players. The United States, United Kingdom and France issued a joint statement noting that they (like many other Powers) had not taken part in negotiating the TPNW and do not intend ever to become Parties to it; nor do they accept any claim that the instrument “reflects or in any way contributes to the development of customary international law.”

Recent Customary Law and Its Interpretation

The building blocks of customary international law are composed of State practice. But, as the new edition points out, it is necessary to distinguish between conduct of States predicated on opinio juris (“accepted as law”) and consistent behavior deemed by the actor(s) merely as “best practice.” Thus, when it comes to new weapons’ reviews – based on Article 36 of Additional Protocol I and routinely carried out by the United States and its allies – the American position is that “this is done as a ‘best practice’ rather than out of a sense of legal obligation.”

Naturally, as demonstrated in Article 36 reviews of new weapons, “best practice” tends to be drawn into the magnetic field of unratified treaties. Another example is recoil from the use of anti-personnel landmines by a country (like the United States) that is not a Contracting Party to the 1997 Ottawa Convention proscribing them. Although in 2020 the United States had moved away from the Convention’s regime, U.S. policy was realigned in 2022 in a manner more in harmony with the Ottawa strictures.

The general practice of States is often a matter of interpretation. An emblematic illustration is surrender by ground forces to overflying winged military aircraft. In or near the contact zone, helicopters or advancing land units may be summoned to effect capture of the surrendering units. Contrarily, when surrender to aircraft occurs far from the contact zone, capture may not be a practical option. This leads to the question whether ground forces can raise a white flag, with a view to gaining immunity from air strikes as long as enemy winged aircraft constitute a threat, and then – as soon as they disappear over the horizon – resume combat on land. The new edition follows the lead of the 2020 Oslo Manual on Select Topics of the Law of Armed Conflict in concluding that the offer of surrender by ground forces to aircraft may be invalid if capture is not feasible in the prevailing circumstances.

Switching to the principle of proportionality, a cardinal issue is whether all civilians and civilian objects have the same specific weight in the assessment of collateral damage. The matter is debatable, but the new edition is clearly poised on the side of those who do not look at all civilians/civilian objects as of equal standing. Notably, children are not accorded similar treatment compared to adults and civilian hospitals cannot be lumped together with used-car lots.

Proportionality triggers an interesting side issue (linked to the above-mentioned definition of “attacks”) in the sphere of sea warfare. The highly respected 1994 San Remo Manual on Armed Conflicts at Sea maintains that a blockade is prohibited (inter alia) if the injury to the civilian population “is, or may be expected to be, excessive in relation to the concrete and direct military advantage anticipated from the blockade.” The Manual borrows this language from the common exposition of the principle of proportionality (e.g., in Article 51(5) of Additional Protocol I). The problem that surfaces is that, whereas the principle of proportionality is restricted in scope to “attacks,” the imposition of blockade by itself cannot be regarded as coming under this rubric.

Sea warfare in general has gained greater attention in the new edition, among other reasons in consequence of a reemergence of prize law in recent State practice (Israeli case law). Air warfare is highlighted as well, predicated on the Harvard Manual on the subject. For the first time, hostilities in outer space, too, attract some scrutiny. Thus, it is pointed out that assessment of collateral damage (in the exercise of the principle of proportionality) should take into consideration the expected impact of space debris – caused by a lawful attack against a military objective – on civilian satellites and stations.. Given the increasing attention paid nowadays to cyber warfare (notwithstanding the paucity of clear-cut State practice), the text also brings more to the fore topics like the applicability of the construct of military objectives to intangible computer data.


The new edition is glued to the lex lata. It is primarily designed for practitioners whose focus is the jus in bello as it is, rather than as it might be or should have been. Although written by an academic, there is no excess of what may be termed “academism” in the text.


Yoram Dinstein is Professor Emeritus, Tel Aviv University (Israel); Member, Institut de Droit International; and former Stockton Professor, Naval War College (1999–2000, 2002–2003).


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