In international law, the principle of non-intervention includes, but is not limited to, the prohibition of the threat or use of force against the territorial integrity or political independence of any state (Article 2.4 of the Charter). The principle of non-intervention in the internal affairs of States also signifies that a State should not otherwise intervene in a dictatorial way in the internal affairs of other States. The International Court referred in the Nicaragua case to “[t]he element of coercion, which defines, and indeed forms the very essence of, prohibited intervention” (ICJ Reports 1986, p. 108, para. 205). As Oppenheim's International Law puts it, "the interference must be forcible or dictatorial, or otherwise coercive, in effect depriving the state intervened against of control over the matter in question. Interference pure and simple is not intervention" (Vol. I, 9th ed., 1992, p. 432). Butthe extent to which acts other than the use of force are, or should be, prohibited is uncertain. Intervention (even military intervention) with the consent, properly given, of the Government of a State is not precluded. The more common term is “non-intervention”, though “non-interference” also appears in the texts. The latter may suggest a wider prohibition, though in most contexts the two terms seem to be used interchangeably.
Vattel is credited with being the first to formulate a principle of non-intervention (Droit des gens ou principes de la loi naturelle, 1758, vol 1, para. 37). But whether the principle was reflected in the practice of States remained doubtful well into the Nineteenth Century (see for example, the Holy Alliance). Among early treaty formulations of the principle was Article 15 (8) of the Covenant of the League of Nations and the Montevideo Convention on Rights and Duties of States of 1933, which prohibited "interference with the freedom, the sovereignty or other internal affairs, or the processes of the Governments of other nations," together with the Additional Protocol on Non-Intervention of 1936. During the Cold War the Socialist countries in the Soviet bloc were particularly insistent on the principle of non-intervention, but so too were the colonial Powers in the early decades of the United Nations and later the many newly independent States. With the evolution of the right of self-determination and the development of international human rights law, the absolute nature of the principle has greatly diminished. The notion of "responsibility to protect" may represent a further inroad.
There is no doubt that the principle of non-intervention remains a well-established part of international law. The prohibition of intervention "is a corollary of every state's right to sovereignty, territorial integrity and political independence" (Oppenheim's International Law, p 428). The Friendly Relations Declaration [UNGA res. 2625(XXV) 1970]includes a whole section on 'The principle concerning the duty not to intervene in matters within the domestic jurisdiction of any State, in accordance with the Charter.' The UN General Assembly adopted a Declaration on the Inadmissibility of Intervention and Interference in the Domestic Affairs of States (UNGA resolution 2131 (XX) 1965). The International Court was in no doubt about the existence of the principle in the Nicaragua case. In the Corfu Channel case (Merits, 1949), the International Court regarded “the alleged right of intervention as the manifestation of a policy of force, such as has, in the past, given right to the most serious abuses and as such cannot, whatever be the present defects in international organization, find a place in international law” (ICJ Reports 1949, p. 35). As the International Court of Justice said in its 1986 judgment in the Nicaragua case, "[t]he principle of non-intervention involves the right of every sovereign State to conduct its affairs without outside interference; though examples of trespass against this principle are not infrequent, the Court considers that it is part and parcel of customary international law. [ ...] international law requires political integrity [ ... ] to be respected" (ICJ Reports 1986, p.106, para. 202). It went on to say that "the principle forbids all States or groups of States to intervene directly or indirectly in the internal or external affairs of other States" and that "a prohibited intervention must accordingly be one bearing on matters in which each State is permitted, by the principle of State sovereignty, to decide freely. One of these is the choice of a political, economic, social and cultural system, and the formulation of foreign policy. Intervention is wrongful when it uses methods of coercion in regard to such choices, which must remain free ones. [ ... ] the element of coercion [ ,,, ] defines, and indeed forms the very essence of, prohibited intervention" (para. 205). In DRC V. Uganda (2005), the Court noted that Nicaragua had “made it clear that the principle of non-intervention prohibits a State “to intervene , directly or indirectly, with or without armed force, in support of the internal opposition within a State” ” (ICJ Reprts 2005, para. 164).
Article 2.7 of the Charter of the United Nations provides that – "Nothing contained in the present Charter shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any state or shall require the Members to submit such matters to settlement under the present Charter; but this principle shall not prejudice the application of enforcement measures under Chapter VII." Practice under this provision has developed over time (see Higgins 1963), and its practical importance is by now significantly reduced. If the existence of the principle of non-intervention in the internal affairs of States is beyond doubt, its exact content is far from clear. In the Nicaragua case, the International Court considered only those aspects of the principle that appeared relevant to the dispute before it (para. 205). Apart from the prohibition on the use of force (Article 2.4 of the UN Charter), it is difficult to be categorical about what is, and what is not, prohibited by the principle. Much may depend upon the context, and on relations between the States, the general state of society in the States concerned and their level of political development. For example, it seems to be still well-established the diplomats should not interfere in the internal affairs of the State to which they are accredited. But even here, as Denza points out, ""[w]ith the greater emphasis in modern international relations on the encouragement and protection of human rights in other States, conflicts between the diplomatic duty of non-interference and the objective of promoting observance of human rights are frequent" (E Denza, Diplomatic Law (3rd ed., 2008, 465-6). The principle of non-intervention and the limits on a State's jurisdiction can be seen as related. Thus, when the United States sought to impose obligations on foreign companies extraterritorially in support of its own foreign policy objectives, this may be seen as improper intervention in the affairs of the States whose companies are affected and lead to counter-measures by them (protection of trading interests). Among other activities which, depending on the circumstances, may contravene the principle of non-intervention are interference in political activities (such as through financial or other support for particular political parties, comment on upcoming elections or on the candidates; seeking to overthrow the government - so-called 'regime change'). Whether there is an exception to the principle of non-intervention in the case of assistance to peoples seeking to exercise the right of self-determination remains controversial, and was not dealt with in Nicaragua. In recent years there are some who seem to act on the assumption that the export of a political system, or even regime change, is not excluded: see for example, the 1998 US Iraq Liberation Act, which called on the United States “to support efforts to remove the regime headed by Saddam Hussein from power in Iraq and to promote the emergence of a democratic government to replace that regime.” But this is a minority view. Humanitarian intervention seems to have gained ground in recent years, but likewise remains very controversial. What should be (and largely is) uncontested is that States and international organizations are entitled to criticize the human rights situation in other countries.
Corfu Channel (Albania v. United Kingdom) (Merits) ICJ Reports (1949) Nicaragua (Nicaragua v. United States) (Merits) ICJ Reports (1986) Armed Activities on the Territory of the Congo (DRC v. Uganda (Merits) ICJ Reports (2005) A.Thomas, A.J. Thomas, Non-Intervention: The Law and its Import in the Americas (1956) R. J. Vincent, Non-Intervention and International Order (Princeton University Press, Princeton, 1974). Hedley Bull (ed.), Intervention in World Politics (Oxford University Press, Oxford, 1988). Lori Fisler Damrosch, “Politics across Borders: Non-Intervention and Nonforcible Influence over Domestic Affairs” 83 American Journal of International Law (1989) pp. 1-50. Maziar Jamnejad and Michael Wood, “The Principle of Non-Intervention” 22 Leiden Journal of International Law (2009) pp. 345-381. P. Kunig, “Intervention, Prohibition of”, in Max Planck Encyclopedia of Public International Law (2012)