This project will illuminate and seek to rectify a critical blindspot in international humanitarian law governing armed conflict. International humanitarian law focuses on whether civilian harms are “excessive” in each individual attack, but fails to account for cumulative civilian harm over the course of a conflict both with respect to civilian harm across many attacks, as well as the aggregate and emergent effects of prolonged exposure to armed conflict. One of the key anticipated intellectual merits of this project is the development of a new standard of “strategic proportionality” that should apply in addition to current international humanitarian law requirements, according to which belligerents must balance cumulative civilian harm against their clearly defined strategic objectives. In addition, the research will illuminate how decision-makers and conflict-affected populations currently think about cumulative civilian harm. Through this research, the project will deepen understanding of how those who use force and are affected by it view civilian protection under international humanitarian law. The research ideally will culminate in the articulation of a civilian-centered, action-guiding legal and policy framework to govern cumulative civilian harm. <br/><br/>Excessive civilian harm in war is often a result of non-compliance with the laws of war, yet it can also stem from international law’s failure to account for cumulative civilian harm. Legal experts have argued that total civilian casualty numbers do not determine whether military operations are lawful and that many harmful effects of war are beyond the reach of law. This project is animated by a belief that international law should not be silent on these issues. It responds to requests from senior political and military practitioners from different countries who have reached out to stress the urgent need for action-guiding rules on cumulative civilian harm. The research will focus on four key work products: (1) desk research into case, treaty law, and military manuals, along with a systematic review of existing scholarship; (2) interviews with former and current senior military and political decision-makers to determine if and how cumulative civilian harm is considered in decision-making; (3) field research via survey experiments in conflict zones to determine attitudes towards cumulative civilian harm; and (4) development of a legal and policy framework to enable political decision-makers to account for cumulative civilian harm.<br/><br/>This proposal is awarded under the SBE-UKRI Lead Agency Opportunity.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.