Recent developments surrounding the Democratic People’s Republic of Korea (DPRK) have highlighted the possibility of conflict on the Korean Peninsula. The United States of America’s (U.S.) military options relative to the DPRK — as outlined in a 2017 Congressional Research Service report — raise major legal and just war theory considerations, specifically with regards to a U.S. first strike and the first use of nuclear weapons.

The Legality of a U.S. First Strike

The Korean Armistice Agreement does not clearly establish the applicability of international law governing the recourse to force (jus ad bellum) due to repeated and deliberate violations of the armistice agreement. United Nations’ (U.N.) Security Council approval of the use of force pursuant to Article 42 of the Charter would be unlikely to occur, as competitors of the United States — namely the Russian Federation and the People’s Republic of China — would presumably utilize their vetoes to restrict the legality of a U.S. first strike. In spite of the forecasted restrictions with the invocation of Article 42 and the restrictive language of Article 51 of the U.N. Charter, contemporary international law has largely established anticipatory self-defense as a valid legal rationale to use force. This is attributable to the Caroline Case, which established that preemptive violence is justifiable if there is a demonstrable “necessity of self-defense” which is “instant, overwhelming, leaving no choice of means, and no moment for deliberation.” Such demonstrability, which is established through corroborated intelligence gathering and analysis, legitimizes preemption. All kinetic U.S. military options must be conducted in genuine anticipation of an imminent and unavoidable attack by the DPRK in order to be considered lawful.

Further nuclear and missile testing would not be sufficient legal justification to support a “necessity of self-defense,” as any announcement of resumed missile and nuclear testing is not in-and-of-itself indicative of an immediate incoming strike against U.S. forces. Therefore, a U.S. first strike conducted in such conditions would be outside the scope of anticipatory self-defense, regardless of whether airstrikes are of a limited or large scale relative to the principle of proportionality.

The Ethics of a U.S. First Strike

Although a potential US first strike raises moral dilemmas not too dissimilar from corresponding legal considerations, the validity of ethical justifications — for both limited and large-scale strikes — is contingent on the intention of the DPRK’s nuclear weapons and missile programs. According to Just War Theorist Michael Walzer’s classic Just and Unjust Wars, aggression should be actively combatted and is “the name give[n] to the crime of war” which often begins “without shots being fired or borders crossed.”[1] While the primary legal determinant with any first strike is the status of the imminent attack, Walzer develops the ethical determinant around the point of sufficient threat, which he defines as “a manifest intent to injure, a degree of active preparation that makes that intent a positive danger, and a general situation which waiting, or doing anything other than fighting, greatly magnifies the risk.”[2] The constraining nature of these criteria is further defined through Walzer’s recognition of legitimate self-defense even “in the (probable) absence of any immediate intention to launch such an invasion or attack.”[3] Given the DPRK’s self-disclosed development of nuclear strike capabilities, choosing not to fight greatly magnifies risk, since the DPRK is likely one technical step away from successfully developing a nuclear delivery vehicle capable of targeting the United States.

The unknown strategic intent creates ambiguity as to whether or not the DPRK’s testing constitutes a ‘manifest intent to injure’ or a ‘positive danger.’ An attempt by the DPRK to establish deterrence would not meet the criterion of ‘positive danger’ or a ‘manifest intent to injure;’ however, state press-releases indicating as such are not always indicative of a state’s true intent. The intent for armed aggression is conditional on the adversarial actor’s final goal and respective awareness of probable consequences. A strategic intent beyond nuclear dissuasion — i.e. compellence vis-à-vis newfound nuclear weapon capabilities which credibly and gravely endangers U.S. territorial integrity and political independence through the threat of attack at any time — must be present in order to provide a just war rationale for both first strike options. If intelligence assessments genuinely and verifiably anticipated an adequate intention for compellence in the DPRK’s further acquisition of nuclear weapons, the United States would be ethically justified in proportionally scaling preemptive violence to halt or eliminate DPRK missile and nuclear programs, as “there are threats with which no nation can be expected to live.”[4] Emphasis must be placed on the use of the words ‘genuinely’ and ‘verifiably,’ as there are many historical examples of preventive action justified as preemption. While a credible nuclear effort to forcibly compel another state would provide ethical justification for a proportional first strike, such an event would be of extraordinary circumstance. During the 1960s, many predictions indicated that between 20-30 states would possess nuclear weapons within two decades. The significant magnitude of these projections did not come to fruition. Although partially attributable to other factors, such as the non-proliferation regime, an analysis of this trend — within Dr. Kenneth Waltz’s model of defensive realism, as outlined through his dialogue with Dr. Scott Sagan in The Spread of Nuclear Weapons: An Enduring Debate — inductively implies the “reliability of defense and deterrence” and, by extension, the weaknesses of compellence. In other words, Waltz stipulates that widespread proliferation would be evidence that “nuclear weapons make the offense more effective and the blackmailer’s threat more compelling.”[5]

The Legality of U.S. First Use

The first use of nuclear weapons is legally permissible under strict circumstances. In 1996, the International Court of Justice (ICJ) affirmed the lawful possession of nuclear weapons along with three factors governing the lawfulness of their conditional use. Regardless of whether or not the deployed weapon system is of a conventional or nuclear nature, the legality of the use of force is always contingent on either Article 51 and Article 42 of the U.N. Charter or the contemporary legal understanding of anticipatory self-defense. The principle of proportionality, which states that measures of self-defense must be proportional in addressing the initial provocation, would be of increased consideration due to the destructive potential of nuclear weapons. International humanitarian law is also a substantial governing factor. While the United States Senate has not ratified Additional Protocol I to the Geneva Conventions or acknowledge its respective applicability to the use of nuclear weapons — including but not limited to codified principles of distinction (Article 51.2), proportionality (Article 51.5(b)), and precaution (Article 57.2(a)(ii)), as well as prohibitions on indiscriminate attacks (Article 51.4) and belligerent reprisals (Article 51.6) — the Obama and Trump Administrations have upheld compliance with fundamental principles and customs not dissimilar from those codified within Additional Protocol I, albeit minus the prohibition of belligerent reprisals. These factors seemingly indicate that a U.S. first use of nuclear weapons would be legal if a) preemptively conducted to halt an incoming attack by the DPRK, b) operationally tailored to sufficiently defend against the incoming attack while curtailing unnecessary collateral damage, and c) meeting the standards of international humanitarian law.

A hypothetical scenario, with verified intelligence suggesting the imminent and hostile launch of a nuclear-tipped ballistic missile from a hardened silo, would likely permit the legal U.S. first use of nuclear weapons in proportional counter-force targeting. However, the codified principle of precaution and the principle of necessity dictate that munitions with an appropriate probability of success and of the lowest necessary force — i.e. conventional weapons or the lowest yield nuclear weapons possible — should be employed for lawful use. Additionally, any population centers within the radius of the bomb’s effects would need to be accounted for relative to the principle of proportionality.

The Ethics of U.S. First Use

Although the first use of nuclear weapons would be lawful under certain circumstances, it would most likely be ethically impermissible. The use of nuclear weapons in counter-value targeting grossly violates normative just war principles of noncombatant immunity and due care. Arguments to dismiss the governing set of ethics, such as reprisals and supreme emergency exemptions, are moot. Regardless of the debate surrounding the ethical validity of reprisals, a reprisals-based justification for the use of nuclear weapons would be inapplicable based on their ex post character. This post examines potential U.S. first use, not the validity of moral judgements governing a second strike. Walzer’s exceptions of supreme emergency would also be inapplicable, as conflict with a DPRK possessing upgraded and demonstrated nuclear capabilities would still not threaten the United States or its allies with the destruction of their respective political communities. Walzer argues for the ethical impermissibility of tactical and counter-force uses of nuclear weapons as well, stating that a) the collateral damage of nuclear weapons inherently violates the limits of proportionality and b) tactical and counter-force uses of nuclear weapons risks unrestricted escalation. Despite its historical context in the Cold War, Walzer’s extension of ethical impermissibility holds contemporary validity, albeit with certain modifications.

Understandably, given that his book was published in 1977, Walzer was not able to forecast the improved accuracy and lower yields of contemporary nuclear weapons. Nonetheless, this does not take away from the fact that Walzer fails to address the technical revolution of nuclear weapons while arguing for the ethical impermissibility of counter-force targeting. The argument’s basis on the limits of proportionality — the number of casualties relative to the goals of the war and the number of people killed by individual actions — is fundamentally challenged by these technical developments. Instead, the proportionality standard should be judged on a case-by-case basis relative to the target’s importance and respective war aims, the nuclear weapon’s yield and detonation altitude (high altitude bursts, air bursts, surface bursts, and sub-surface bursts), and the number of civilian casualties from the blast and fallout.

Walzer’s second argument, based on the inherent risks of nuclear weapons in conflict escalation, can be further expanded beyond its original backdrop of U.S.-Soviet dynamics. The destructive power of nuclear weapons is not the only escalatory factor in a tactical and counter-force context. A primary driver of escalation would be the perception that nuclear weapons are inherently different, solidified through a tradition of non-use. The use of nuclear weapons would foreseeably nuclearize the immediate conflict while eroding the nuclear taboo beyond repair, setting a dangerous new precedent for the use of nuclear weapons in future conflicts while incentivizing proliferation and widespread use around the world. Actions that directly result in any of these consequences — relative to the immediate conflict and the following consequences on the international community — would not be ethical. To suggest ethical impermissibility for breaking normative state practice with direct future implications, however, is to suggest a revision to Walzer’s outlook of just war theory and the traditional scope of the principle of proportionality. Through an extension of moral accountability to long-term strategic consequences, such moral judgements would further encourage the creation of more principled war plans and reciprocal practices of non-use among states.

Concluding Thoughts

Announcements of resuming DPRK missile and nuclear testing would not legally justify a U.S. first strike. Utilizing just war theorist Michael Walzer’s model of aggression, strikes of any nature would not be ethically justified unless the DPRK is set to use its newfound nuclear capabilities to severely coerce and actively endanger U.S. political integrity, given the restricted reach of the DPRK’s military capabilities. While the constrained first use of nuclear weapons can be legally justified under select conditions, it would be ethically impermissible due to its consequences for the international norm of non-use.

These legal and ethical concerns governing the use of force serve as a significant benchmark within the contemporary rules-based order. This is of special consequence within the context of the Korean Peninsula, considering its potential strategic implications for future U.S. conduct within East and South Asia. A number of important factors apart from those discussed in this post must be considered when making decisions of such a magnitude; even so, Washington should be cognizant of the potential for controversial actions to undermine the liberal international order and empower emerging competitors.

[1] Michael Walzer, Just and Unjust Wars 51, 74 (4th ed., 1977).

[2] Id. at 81.

[3] Id. at 85.

[4] Id.

[5] Scott Sagan & Kenneth Waltz, The Spread of Nuclear Weapons 6 (3rd ed., 2006).

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Ethan Lee is a student at Stanford University studying Political Science and History. He is interested in US foreign policy, the law of war, and the use of soft power in entertainment and media.