Inventing Proportionality

The principle of proportionality—the idea that the foreseeable harm of a military action should not outweigh the value of the action’s objective—is now standard in American foreign policy discourse and military planning. At West Point last year, Barack Obama emphasized that the future use of American force would need to be accompanied by “tough questions about whether our actions are proportional.” And in his earlier Nobel Peace Prize Lecture, he traced the history of proportionality (and other just war concepts) back to medieval “philosophers and clerics and statesmen” who sought “to regulate the destructive power of war.”

But President Obama’s invocation of a long history of proportionality is misleading. The concept only became familiar during the twentieth century, and for much of that time the United States opposed its incorporation into the laws of war. By the 1970s, however, America became a champion of the rule of proportionality, leading efforts to have it enshrined within the first Additional Protocol to the Geneva Conventions (1977) and, more generally, within national and global public opinion. That remarkable shift, this paper argues, was prompted by the Vietnam War, during which appealing to the principle of proportionality emerged as a way to rationalize U.S. actions in a disorienting, asymmetric military environment.

The first part of this paper traces the rise of the concept of proportionality in the thought of jurists and humanitarians during the twentieth century. The second part uncovers and examines the use of the principle during the Vietnam War. The third part analyzes the contentious discussions on proportionality during the negotiations for the Additional Protocols, emphasizing the contingent nature of its codification into international law. In sum, the paper aims to reveal more clearly the surprisingly recent history of this bedrock principle of wartime conduct.