State responsibility is one of the elements that go to assessing whether an action is in conformity with the principles of necessity and proportionality.333 A State acting in self-defence is “totally restrained” by an international obligation if that obligation is expressed or intended to apply as a definitive constraint even to States in armed conflict.334 (5) The essential effect of article 21 is to preclude the wrongfulness of conduct of a State acting in self-defence vis-à-vis an attacking State. But there may be effects visà-vis third States in certain circumstances. In its advisory opinion on the Legality of the Threat or Use of Nuclear Weapons, the Court observed that: [A]s in the case of the principles of humanitarian law applicable in armed conflict, international law leaves no doubt that the principle of neutrality, whatever its content, which is of a fundamental character similar to that of the humanitarian principles and rules, is applicable (subject to the relevant provisions of the United Nations Charter), to all international armed conflict, whatever type of weapons might be used.335 The law of neutrality distinguishes between conduct as against a belligerent and conduct as against a neutral. But neutral States are not unaffected by the existence of a state of war. Article 21 leaves open all issues of the effect of action in self-defence vis-à-vis third States. (6) Thus, article 21 reflects the generally accepted position that self-defence precludes the wrongfulness of the conduct taken within the limits laid down by international law. The reference is to action “taken in conformity with the Charter of the United Nations”. In addition, the term “lawful” implies that the action taken respects those obligations of total restraint applicable in international armed conflict, as well as compliance with the requirements of proportionality and of necessity inherent in the notion of self-defence. Article 21 simply reflects the basic principle for the purposes of chapter V, leaving questions of the extent and application of self-defence to the applicable primary rules referred to in the Charter. Article 22. Countermeasures in respect of an internationally wrongful act The wrongfulness of an act of a State not in conformity with an international obligation towards another State is precluded if and to the extent that the act constitutes a countermeasure taken against the latter State in accordance with chapter II of Part Three. Commentary (1) In certain circumstances, the commission by one State of an internationally wrongful act may justify another State injured by that act in taking non-forcible countermeasures in order to procure its cessation and to achieve reparation for the injury. Article 22 deals with this situation from the perspective of circumstances precluding 333 Ibid., p. 242, para. 30. See, e.g., the Convention on the Prohibition of Military or any Other Hostile Use of Environmental Modification Techniques. 335 I.C.J. Reports 1996 (see footnote 54 above), p. 261, para. 89. 334 75 wrongfulness. Chapter II of Part Three regulates countermeasures in further detail. (2) Judicial decisions, State practice and doctrine confirm the proposition that countermeasures meeting certain substantive and procedural conditions may be legitimate. In the Gabčíkovo-Nagymaros Project case, ICJ clearly accepted that countermeasures might justify otherwise unlawful conduct “taken in response to a previous international wrongful act of another State and … directed against that State”,336 provided certain conditions are met. Similar recognition of the legitimacy of measures of this kind in certain cases can be found in arbitral decisions, in particular the “Naulilaa”,337 “Cysne”,338 and Air Service Agreement339 awards. (3) In the literature concerning countermeasures, reference is sometimes made to the application of a “sanction”, or to a “reaction” to a prior internationally wrongful act; historically the more usual terminology was that of “legitimate reprisals” or, more generally, measures of “self-protection” or “self‑help”. The term “sanctions” has been used for measures taken in accordance with the constituent instrument of some international organization, in particular under Chapter VII of the Charter of the United Nations—despite the fact that the Charter uses the term “measures”, not “sanctions”. The term “reprisals” is now no longer widely used in the present context, because of its association with the law of belligerent reprisals involving the use of force. At least since the Air Service Agreement arbitration,340 the term “countermeasures” has been preferred, and it has been adopted for the purposes of the present articles. (4) Where countermeasures are taken in accordance with article 22, the underlying obligation is not suspended, still less terminated; the wrongfulness of the conduct in question is precluded for the time being by reason of its character as a countermeasure, but only provided that and for so long as the necessary conditions for taking countermeasures are satisfied. These conditions are set out in Part Three, chapter II, to which article 22 refers. As a response to internationally wrongful conduct of another State, countermeasures may be justified only in relation to that State. This is emphasized by the phrases “if and to the extent” and “countermeasures taken against” the responsible State. An act directed against a third State would not fit this definition and could not be justified as a countermeasure. On the other hand, indirect or consequential effects of countermeasures on third parties, which do not involve an independent breach of any obligation to those third parties, will not take a countermeasure outside the scope of article 22. (5) Countermeasures may only preclude wrongfulness in the relations between an injured State and the State which has committed the internationally wrongful act. 336 Gabčíkovo-Nagymaros Project (see footnote 27 above), p. 55, para. 83. 337 Portuguese Colonies case (Naulilaa incident), UNRIAA, vol. II (Sales No. 1949.V.1), p. 1011, at pp. 1025–1026 (1928). 338 Ibid., p. 1035, at p. 1052 (1930). 339 Air Service Agreement (see footnote 28 above). 340 Ibid., especially pp. 443–446, paras. 80–98.