The Illegality of Targeting Civilians by Way of Belligerent Reprisal: Implications for U.S. Nuclear Doctrine

Although the United States has, in recent years, unequivocally accepted the notion that international humanitarian law (IHL) applies to its nuclear operations, there’s a catch. To date, the U.S. government has not declared that it no longer reserves a purported right to target civilians by way of reprisal, in response to an unlawful attack against U.S. or allied civilians. As we have argued elsewhere, and as Adil Haque recently called on the Biden administration to do, it is time for the United States to acknowledge that customary international law today prohibits targeting civilians in reprisal for an adversary’s violations of the law of war. The Biden administration is conducting a nuclear posture review, which will provide an opportunity to clarify its position. Even without reliance on the doctrine of belligerent reprisal, the United States can credibly deter illegal attacks against civilians through responsive strikes that do not target the adversary’s civilians and that comply with IHL.

The Application of IHL to the use of Nuclear Weapons

The United States has not always been clear or consistent regarding the application of IHL to the use of nuclear weapons. For instance, in 1977, when the United States signed Additional Protocol I to the 1949 Geneva Conventions Relating to the Protection of Victims of International Armed Conflict (Protocol I), it declared that the rules established by the Protocol “were not intended to have any effect on and do not regulate or prohibit the use of nuclear weapons.” In the intervening decades, however, international consensus has emerged that IHL would apply to any use of nuclear weapons. By 2013, the Obama administration, explicitly embraced the notion that all nuclear weapons use plans “must …be consistent with the fundamental principles of the Law of Armed Conflict.” The United States reaffirmed, in the Trump administration’s 2018 Nuclear Posture Review, that any U.S. nuclear military operations “would adhere to the law of armed conflict.” This means that the United States accepts, among other IHL obligations, that its nuclear targeting policies must apply the principle of distinction (that it may not direct attacks against the civilian population or civilian objects), and the principle of proportionality (that it may not launch attacks that would cause incidental civilian harm that is excessive in relation to the concrete and direct military advantage anticipated from the attacks). The United States also accepts that it is legally required, under the principle of precaution, to take all feasible measures to minimize incidental damage to civilian populations and civilian objects...