D. H. Dilbeck: What is a Just War? How the Union’s “Lieber Code” Answered a Perennial Question

A More Civil War cover imageDuring the Civil War, Americans confronted profound moral problems about how to fight in the conflict. In his innovative book, A More Civil War: How the Union Waged A Just War, D. H. Dilbeck reveals how the Union sought to wage a just war against the Confederacy. He shows that northerners fought according to a distinct “moral vision of war,” an array of ideas about the nature of a truly just and humane military effort. Dilbeck explores how Union soldiers abided by official just-war policies as they battled guerrillas, occupied cities, retaliated against enemy soldiers, and came into contact with Confederate civilians.

In today’s guest post, Dilbeck explains how Lieber’s code for the Union Army attempted to define “just war” during the American Civil War.


We’re living through an age of rapid innovation in military technology. To cite only one of many possible examples, the swift embrace of “Unmanned Aerial Vehicles” over the past decade has transformed the United States’ military presence throughout the world. And yet, despite all the revolutions in technologies and tactics, an old question remains with us: What is a just war?

A century and a half ago, Civil War Americans pondered this question. Today’s wars would be practically unrecognizable to them, but the underlying moral dilemmas wrapped up in modern military conflicts would surely seem all too familiar. Historians have written a lot lately about how terribly destructive the Civil War was—a scholarly effort not without merit. But quite often overlooked are the sincere efforts made by Civil War Americans to define and wage a just war.

The most consequential example to do exactly that resulted in “Instructions for the Government of Armies of the United States in the Field,” a military code of conduct for Union soldiers issued in May 1863 by President Abraham Lincoln as General Orders No. 100. The document quickly became known informally as the Lieber code, named after its principal author, Francis Lieber.

Lieber was a Berlin-born jurist and scholar who taught in South Carolina from 1835-1856, but was professor of history and political economy at Columbia College in New York City at the outbreak of the Civil War. Almost as soon as the war began, Lieber (who wrote widely on the laws of war in the antebellum era) saw the need for something like the code he eventually drafted. The traditional just-war framework distinguishes between jus in bello, just conduct in war and jus ad bellum, legitimate reasons for engaging in war.

Lieber never doubted that the war to save the Union met the dictates of jus ad bellum; it was unquestionably just in that sense. But in April 1861 it remained unknowable whether Federal armies would also abide by the laws of war governing jus in bello. Would the war to save the Union that had begun a just war remain a just war? By late 1862, Lieber successfully persuaded the Lincoln administration to establish a committee to draft something like the code of military conduct that he envisioned. Lieber was appointed a member of the committee and, by all accounts, overwhelmingly responsible for the code the committee ultimately produced.

The Lieber code consisted of 157 articles, many as short as a single sentence or two, that collectively attempted to offer soldiers a succinct yet comprehensive guide to just conduct in war. The topics addressed in the Lieber code range widely—from guerrilla warfare to martial law, to retaliation, to flags of truce, to the treatment of civilians and prisoners of war, among many others. But the code’s goal remained to define, as best as possible, the boundaries of acceptable conduct in war—according to existing legal and moral traditions on the prosecution of war.

So how exactly, then, did Lieber’s code define a justly waged war? According to the code, what made a just war just, and when exactly did a military effort become unjust in its prosecution? Two particular articles nicely reveal the vision of just warfare that pervaded the entire code and gave it coherence.

According to article twenty-nine: “The more vigorously wars are pursued, the better it is for humanity. Sharp wars are brief.” Here, somewhat buried in the code, was perhaps Lieber’s core assumption about just warfare: that the most humane and moral wars were usually the ones most vigorous in their prosecution, which Lieber defined as a military effort that deployed all possible means (within certain restrictions) to achieve victory as swiftly as possible. Lieber assumed that a vigorous war, thus defined, ultimately would be briefer, and therefore an occasion for less suffering and devastation. As he wrote elsewhere of war, “the shorter it is the better; and the intenser it is carried on, the shorter it will be.” In that way, the vigorous war was a humane war. In its particular articles, Lieber’s code undeniably authorized a potentially immense degree of violence and destruction—but all with the express purpose of more quickly ending the war victoriously.

A second essential just-war claim came in article fifteen: “Men who take up arms against one another in public war do not cease on this account to be moral beings, responsible to one another and to God.” Lieber certainly believed that any truly just war would effectively balance the principles contained in articles fifteen and twenty-nine. Although the code advised the Union army to wage a “sharp” war to end the conflict quickly, it also simultaneously insisted that all belligerents in war must still adhere to certain moral restraints in their actions. War did not erase the moral responsibilities incumbent on all people, Lieber believed. For that reason, some behaviors were never permissible according to the code—for example, the use of poison or acts of “wanton devastation.”

Even though Lieber’s code justified immense destruction in the name of military necessity, its overall intended effect was to constrain the war’s devastation and suffering. In that way, it proved to be the most lucid effort to emerge from the Civil War to explain how an army might triumph swiftly in a military conflict while still also abiding by its deepest moral obligations.

D. H. Dilbeck is assistant professor of history at Oklahoma Baptist University.