Possible Exceptions to Intervening Cause Justifications of the Legality of Nuclear Weapons

In justifying the continued legality of nuclear weapons, the United States has argued that smaller-scale nuclear weapons tailored to their targets may retain their legality because they are more controllable.[1] The controllability argument depends on the assumption that if the initial strike results in counter-strikes that themselves violate international law, such escalation is beyond the legal responsibility of the first-strike party.[2] The crux of this assumption is that the initial strike cannot have legally caused the subsequent illegal strikes, presumably because the subsequent strike is an intervening cause that breaks the chain of causation.[3] While a theory of intervening cause appears to serve prominently as the basis for the U.S. position on escalation risk,[4] International Criminal law (ICL) has not thoroughly developed the concept of intervening cause.[5] By plugging richly developed U.S. common law theories of principal liability causation into an otherwise ICL-centered war crimes framework, a true test can be carried out.[6]

The relevant facts concerning U.S. nuclear weapons policy consist of the availability of launch on warning tactics and the extreme circumstances in which the use of nuclear weapons is envisioned. Launch on warning, which remains an option for the U.S. President, empowers the United States to launch nuclear retaliatory strikes in the narrow window of time between the detection of an incoming strike and its ultimate impact.[7] Based on one analysis, a preliminary assessment of sensor data is supposed to arrive with decision-makers within three minutes.[8] Regarding extreme circumstances, it is understood that the use of nuclear weapons, even if limited to smaller-scale nuclear weapons, would likely occur in an extreme scenario and thus under duress.[9]

Under U.S. law, an intervening cause breaks the chain of causation only if it was freely chosen, meaning it was neither involuntarily nor under undue duress.[10] Involuntary conduct is typically associated with reflexes, seizures and the like,[11] but has been expanded to include contrived involuntariness, which arises where a defendant has created the conditions of their involuntariness.[12] For example, a defendant who killed four children in a car accident due to his epileptic seizure was denied the defense of involuntariness—and thus was judged to have caused the deaths—because the court found he was aware of the risk such a seizure would occur.[13]

Conduct is essentially considered involuntary if performed under sufficient duress. In Moyer, the owner of a gas station accidentally killed his employee while firing a revolver in self-defense at a person robbing the gas station. The jury was instructed that the defendant robber could be held to have caused the death if it found that the shots were fired to frustrate the robbery. The Pennsylvania court upheld this instruction on the grounds that “the act of defending oneself is a primal human instinct and is also the right and duty of persons threatened with aggression.”[14]

Setting aside whether a subsequent escalatory strike fulfills the relevant act and mens rea requirements, contrived voluntariness and duress provide two avenues for establishing causation under the relevant facts. In terms of contrived voluntariness, the hair-trigger policy of launch on warning could be viewed as a way in which the U.S. has created conditions in which the use of a nuclear weapon could lead reflexively to mass nuclear war.[15] In terms of duress, considering the intense fog of war generated by the kinds of conflicts in which nuclear weapons use has been contemplated, it seems reasonable to think that a country pondering the use of a nuclear weapon would be under severe duress and threat of aggression.[16]

In conclusion, the concept of intervening cause appears crucial to U.S. nuclear weapons policy,[17] yet the concept is not well-developed in ICL.[18] Applying U.S. intervening cause theory to plug this gap potentially raises questions about the durability of the U.S. legal position on escalation risk.[19]

Philip Parkes is a staff member of Fordham International Law Journal Volume XLVII.

[1] See Written Statement of the Government of the United States of America, Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 1996 I.C.J. at 23 (June 20, 1995) [hereinafter U.S. ICJ Memorandum/G.A. App.] (“It has been argued that nuclear weapons are unlawful because they cannot be directed at a military objective. This argument ignores the ability of modern delivery systems to target specific military objectives with nuclear weapons, and the ability of modern weapons designers to tailor the effects of a nuclear weapon to deal with various types of military objectives. Since nuclear weapons can be directed at a military objective, they can be used in a discriminate manner and are not inherently indiscriminate.”).                                                       

[2] See U.S. Dep’t Of Defense, Department of Defense Law of War Manual §5.12.1.4 (July 2023 update) (“Harm caused by enemy action . . . need not be considered.”). The manual further states, as an example of this situation, that a commander in charge of a nation’s air offenses, in planning their attacks on the enemy, does not need to account for damage to civilians that might occur because of counter-attacks from the enemy that result from the attacks that they direct. Id. (“[A] commander directing an air operation would not need to consider civilians injured or killed by counter-attacks from enemy air defense measures . . . .”).

[3] See id. (“Harm caused by enemy action . . . need not be considered.”) (emphasis added). See also

Joseph Kennedy, A Short and Happy Guide to Criminal Law, 207 (West, 2020) (explaining that the chain of causation is “a metaphorical term that refers to a sequence of causally related actions or events”, that “[w]hen we say that the chain of causation is broken, we mean that we no longer consider the defendant’s acts earlier in the chain to be responsible for the results after the break,” and that intervening causes considered “independent” of the actions of the initial actor—in this case, the U.S. military—often break this chain). The implicit argument is that whatever or whomever is the cause of the final, ultimate destruction of an escalatory nuclear strike, it is not the initial actor. U.S. Dep’t Of Defense, supra note 2, at §5.12.1.4. For additional discussion of the concept of intervening cause, see Wayne LaFave, Principles of Criminal Law, §5.4 (West, 2017).

[4] See U.S. Dep’t Of Defense, supra note 2, at §5.12.1.4.

[5] See M. Cupido, Causation in International Crimes Cases: ReConceptualizing the Causal Linkage, 22-24 (VU University Amsterdam - Faculty of Law, Working Paper, 2020), https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3641283 (“Domestic law . . . focuses on causality questions that are less prominent in the international sphere, such as the issue under which intervening circumstances and acts of third persons break the causal chain.”) (emphasis added). The ICL lack of emphasis on intervening cause questions, and its contrasting deeper development of causation within accessorial modes of liability such as instigation, may stem from the remoteness of criminal actors within the ICL context, a lack of proximity that poses inherent difficulties when resolving questions of causation. Id. at 37 (discussing how, in a typical international crimes case, the empirical link between the accused and the crime is more remote than in a standard criminal case). Unlike principal liability, which raises questions of intervening cause, accessorial liability effectively obviates the need for—and can be viewed as having been created for the very purpose of avoiding—the problem of intervening cause by means of the theory of instigation. See Kadish et al., Criminal Law And Its Processes, 625 (Wolters Kluwer, 10th ed. 2017) (explaining that when “the law of causation is not available to ground the responsibility of the first actor . . . other doctrines must be created to hold responsible those who instigate . . . a crime.”) (emphasis added). Under the theory of instigation, rather than prove that a distant actor causes something bad to happen (in which case the issue of intervening actors might arise), ICL simply asserts that the distant actor induces someone else to cause the bad act. Sliedregt et al., Modes of Liability in International Law, 259 (Cambridge 2019) (defining instigation as when a person prompts another person to commit a crime). In sum, the theory is that ICL has avoided developing intervening cause because instigation provides a workaround that allows it to hold remote actors responsible without addressing the root issue of whether an intervening actor breaks the chain of causation, a state of affairs that would not be a problem were this root issue not the apparent basis for a major nuclear power’s justification for the use of nuclear weapons. U.S. ICJ Memorandum/G.A. App., supra note 1, at 23.

[6] See Kadish et al., supra note 5, at 603-641 (discussing approaches to causation within U.S. law generally).

[7] See, e.g., Frank N. von Hippel, Biden should end the launch-on-warning option, Bulletin of the Atomic Scientists (June 22, 2021), https://thebulletin.org/2021/06/biden-should-end-the-launch-on-warning-option/; The “Launch on Warning” Nuclear Strategy and Its Insider Critics, National Security Archive at George Washington University, (2019), https://nsarchive.gwu.edu/briefing-book/nuclear-vault/2019-06-11/launch-warning-nuclear-strategy-its-insider-critics.

[8] See Bruce Blair, De-Alerting Strategic Forces, in Reykjavik Revisited: Steps Toward a World Free of Nuclear Weapons 47 (George P. Shultz et al. eds., 2007).

[9] See, e.g., Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 1996 I.C.J. 263 (July 8), (Concluding that nuclear weapons are not necessarily illegal in the “extreme circumstance of self-defence” where “survival” of the State is at stake); Dr. W. Andrew Terrill, Escalation and Intrawar Deterrence During Limited Wars in the Middle East, 35, 90 (US Army War College Press, 2009) (describing how senior Israeli leadership went on record to admit the “anxiety never previously experienced” which “gripped” them while facing what some believed to be an existential threat to statehood).

[10] See Kadish et al., supra note 5, at 625-26 (discussing the various circumstances which might render a decision not freely chosen).

[11] See Claire Finkelstein, Involuntary Crimes, Voluntarily Committed, in Criminal Law Theory: Doctrines of the General Part, 143 (Oxford, 2005).

[12] See id. at 146 (“The problem of contrived involuntariness is the most extreme version of a more general problem, namely the problem of defendants who culpably create the conditions of their own involuntariness.”).

[13] See id.

[14] H.L.A. Hart & Tony Honoré, Causation in the Law, 331 (2nd ed. 1985).

[15] See sources cited supra notes 7-8.

[16] See sources cited supra note 9.

[17] See sources cited supra notes 2-4.

[18] See sources cited supra note 5.

[19] See supra notes 15-16 and accompanying text.

This is a student blog post and in no way represents the views of the Fordham International Law Journal.

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