74 Report of the International Law Commission on the work of its fifty-third session preclude wrongfulness, it will be necessary to show that the conduct fell within the limits of the consent. Consent to overflight by commercial aircraft of another State would not preclude the wrongfulness of overflight by aircraft transporting troops and military equipment. Consent to the stationing of foreign troops for a specific period would not preclude the wrongfulness of the stationing of such troops beyond that period.327 These limitations are indicated by the words “given act” in article 20 as well as by the phrase “within the limits of that consent”. (10) Article 20 envisages only the consent of States to conduct otherwise in breach of an international obligation. International law may also take into account the consent of non-State entities such as corporations or private persons. The extent to which investors can waive the rules of diplomatic protection by agreement in advance has long been controversial, but under the Convention on the Settlement of Investment Disputes between States and Nationals of other States (art. 27, para. 1), consent by an investor to arbitration under the Convention has the effect of suspending the right of diplomatic protection by the investor’s national State. The rights conferred by international human rights treaties cannot be waived by their beneficiaries, but the individual’s free consent may be relevant to their application.328 In these cases the particular rule of international law itself allows for the consent in question and deals with its effect. By contrast, article 20 states a general principle so far as enjoyment of the rights and performance of the obligations of States are concerned. Article 21. Self-defence The wrongfulness of an act of a State is precluded if the act constitutes a lawful measure of self-defence taken in conformity with the Charter of the United Nations. Commentary (1) The existence of a general principle admitting selfdefence as an exception to the prohibition against the use of force in international relations is undisputed. Article 51 of the Charter of the United Nations preserves a State’s “inherent right” of self-defence in the face of an armed attack and forms part of the definition of the obligation to refrain from the threat or use of force laid down in Article 2, paragraph 4. Thus, a State exercising its inherent right of self-defence as referred to in Article 51 of the Charter is not, even potentially, in breach of Article 2, paragraph 4.329 327 The non-observance of a condition placed on the consent will not necessarily take conduct outside of the limits of the consent. For example, consent to a visiting force on the territory of a State may be subject to a requirement to pay rent for the use of facilities. While the non-payment of the rent would no doubt be a wrongful act, it would not transform the visiting force into an army of occupation. 328 See, e.g., International Covenant on Civil and Political Rights, arts. 7; 8, para. 3; 14, para. 3 (g); and 23, para. 3. 329 Cf. Legality of the Threat or Use of Nuclear Weapons (footnote 54 above), p. 244, para. 38, and p. 263, para. 96, emphasizing the lawfulness of the use of force in self-defence. (2) Self-defence may justify non-performance of certain obligations other than that under Article 2, paragraph 4, of the Charter of the United Nations, provided that such non-performance is related to the breach of that provision. Traditional international law dealt with these problems by instituting a separate legal regime of war, defining the scope of belligerent rights and suspending most treaties in force between the belligerents on the outbreak of war.330 In the Charter period, declarations of war are exceptional and military actions proclaimed as self-defence by one or both parties occur between States formally at “peace” with each other.331 The 1969 Vienna Convention leaves such issues to one side by providing in article 73 that the Convention does not prejudice “any question that may arise in regard to a treaty ... from the outbreak of hostilities between States”. (3) This is not to say that self-defence precludes the wrongfulness of conduct in all cases or with respect to all obligations. Examples relate to international humanitarian law and human rights obligations. The Geneva Conventions for the protection of war victims of 12 August 1949 and the Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the protection of victims of international armed conflicts (Protocol I) apply equally to all the parties in an international armed conflict, and the same is true of customary international humanitarian law.332 Human rights treaties contain derogation provisions for times of public emergency, including actions taken in self-defence. As to obligations under international humanitarian law and in relation to non-derogable human rights provisions, self-defence does not preclude the wrongfulness of conduct. (4) ICJ in its advisory opinion on the Legality of the Threat or Use of Nuclear Weapons provided some guidance on this question. One issue before the Court was whether a use of nuclear weapons would necessarily be a breach of environmental obligations because of the massive and long-term damage such weapons can cause. The Court said: [T]he issue is not whether the treaties relating to the protection of the environment are or are not applicable during an armed conflict, but rather whether the obligations stemming from these treaties were intended to be obligations of total restraint during military conflict. The Court does not consider that the treaties in question could have intended to deprive a State of the exercise of its right of self-defence under international law because of its obligations to protect the environment. Nonetheless, States must take environmental considerations into account when assessing what is necessary and proportionate in the pursuit of legitimate military objectives. Respect for the environment 330 See further Lord McNair and A. D. Watts, The Legal Effects of War, 4th ed. (Cambridge University Press, 1966). 331 In Oil Platforms, Preliminary Objection (see footnote 208 above), it was not denied that the 1955 Treaty of Amity, Economic Relations and Consular Rights remained in force, despite many actions by United States naval forces against the Islamic Republic of Iran. In that case both parties agreed that to the extent that any such actions were justified by self-defence they would be lawful. 332 As the Court said of the rules of international humanitarian law in the advisory opinion on the Legality of the Threat or Use of Nuclear Weapons (see footnote 54 above), p. 257, para. 79, “they constitute intransgressible principles of international customary law”. On the relationship between human rights and humanitarian law in time of armed conflict, see page 240, para. 25.