(This op-ed was first published in Just Security on May 10, 2021.)

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.

(Continue reading the op-ed on Just Security’s page here.)

Allen Weiner is a Senior Lecturer in Law at Stanford Law School, where he is the Director of the Stanford Program in International and Comparative Law and Director of the Stanford Center on International Conflict and Negotiation.