The obligation of non-intervention, a norm of customary international law prohibits States from intervening coercively in the internal or external affairs of other States. Prohibited intervention was authoritatively defined by the International Court of Justice in the judgment on the merits in the 1986 case Nicaragua v United States:
A prohibited intervention must … 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.[1]
In order for an act, including a cyber operation, to qualify as a prohibited intervention, it must fulfil the following conditions:
The act must bear on those matters in which States may decide freely. The spectrum of such issues is particularly broad and it includes both internal affairs (such as the “choice of a political, economic, social, and cultural system”[1] or the conduct of national elections[2]), and external affairs (“formulation of foreign policy”;[1] “recognition of states and membership of international organisations”[3])—the so-called domaine réservé of States.[4] The content of the domaine réservé is determined by the scope and nature of the State's international legal obligations.
The act must be coercive in nature. There is no generally accepted definition of “coercion” in international law. In this respect, two main approaches have emerged in the cyber context.[5] Under the first approach, an act is coercive if it is specifically designed to compel the victim State to change its behaviour with respect to a matter within its domaine reservé.[6] Under the second approach, in order for an act to qualify as coercive, it is sufficient if it effectively deprives the target State of its ability to control or govern matters within its domaine reservé.[7]
Finally, there has to be a causal nexus between the coercive act and the effect on the internal or external affairs of the target State.[8]
↑See, for example, Katja Ziegler, “Domaine Réservé”, in Rudiger Wolfrum (ed), Max Planck Encyclopedia of Public International Law (OUP 2008) (updated April 2013) (defining the domaine réservé as those “areas where States are free from international obligations and regulation”).
↑See, eg, Dutch Minister of Foreign Affairs, ‘Letter to the President of the House of Representatives on the International Legal Order in Cyberspace – Appendix: International Law in Cyberspace’ (5 July 2019) 3, defining coercion as ‘compelling a state to take a course of action (whether an act or an omission) that it would not otherwise voluntarily pursue’ and noting that ‘[t]he goal of the intervention must be to effect change in the behaviour of the target state’; Germany, ‘On the Application of International Law in Cyberspace: Position Paper’ (March 2021), 5, defining coercion as a situation in which a State’s ‘will is manifestly bent by the foreign State’s conduct’ and noting that ‘the acting State must intend to intervene in the internal affairs of the target State’; see also Tallinn Manual 2.0, commentary to rule 66, para 19 (‘The majority of Experts was of the view that the coercive effort must be designed to influence outcomes in, or conduct with respect to, a matter reserved to a target State.’).
↑See, eg, Australia, ‘Supplement to Australia’s Position on the Application of International Law to State Conduct in Cyberspace’ (2019) 4 (‘A prohibited intervention is one that interferes by coercive means (in the sense that they effectively deprive another state of the ability to control, decide upon or govern matters of an inherently sovereign nature), either directly or indirectly, in matters that a state is permitted by the principle of state sovereignty to decide freely.’); New Zealand, ‘The Application of International Law to State Activity in Cyberspace’ (1 December 2020), para 9(b) (stating that a State cyber activity is coercive if ‘there is an intention to deprive the target state of control over matters falling within the scope of its inherently sovereign functions’); see also Tallinn Manual 2.0, commentary to rule 66, para 19 (‘A few Experts took the position that to be coercive it is enough that an act has the effect of depriving the State of control over the matter in question.’).
↑Tallinn Manual 2.0, commentary to rule 66, para 24 (the exact nature of the causal nexus was not agreed on).
