Does the U.S. military's killing of foreign civilians affect American public support for war? Conventional wisdom in International Relations (IR) and social psychology suggests U.S. military harm to foreign civilians has a minimal impact on public attitudes. Scholars attribute this indifference to the public’s focus on winning wars while minimizing harm to American soldiers and its biases against out-group persons. However, a growing literature in IR argues that civilian harm lowers public support for war because the public has internalized international legal norms and therefore disapproves of U.S. military operations that violate them. Contrary to these perspectives, this dissertation proposes the “moral public” argument in which civilian harm is theorized to trigger moral intuitions that condition public support for war. Using evidence from six original survey experiments, including two studies with nationally representative samples, this study tested whether the intent behind civilian casualties (intentional, foreseeable, accidental) from U.S. counterterrorism airstrikes affects American public support for war. The study revealed three core findings: (1) public support for the use of force decreased as intent shifts from accidental to foreseeable to intentional, demonstrating public concern for civilian harm; (2) moral considerations rather than legal considerations drove this effect, suggesting that moral intuition is a more plausible explanation than the internationalization of international legal norms; and (3) public concern for foreign civilian harm was moderated by considerations of military effectiveness. The project demonstrates how linking research in the cognitive sciences to the study of public opinion enriches the study of international law and the ethics of war.