Should we thank the Great Emancipator for codifying the law of war—or curse him?

For this reason, some people believe that the law of war is meaningless verbiage, propaganda that nations honor in the breach. Countries either disregard the laws altogether or comply with them only when they happen to converge with their military goals.

Witt spends a lot of time trying to debunk this view, and he is surely right that the law of war mattered in the Civil War. The Union and Confederacy generally refrained from slaughtering POWs (although prison conditions were extremely harsh) and even managed to exchange prisoners from time to time. But in some places he goes too far. He says that Sherman’s march obeyed the law of war, albeit not the supposedly rigid “Enlightenment model of war” but the pleasingly flexible Lieber Code, which gave pride of place to that squishy concept of military necessity. This comes dangerously close to saying that Sherman obeyed the law of war because the law of war permitted him to do anything he wanted to do. And if that is true, then the Lieber Code was meaningless verbiage after all.

Other commentators who have written in defense of the law of war—including many international lawyers—believe that it acts as an external constraint on states, and a constraint based on a common morality rather than expedience or self-interest. This constraint serves a moral purpose by limiting the destructiveness of war. In this view, a belligerent will refrain from executing POWs or bombarding towns even when doing so would advance a military purpose because it is morally wrong.  

Another, more pragmatic, view is that the law of war serves as a source of focal points for mutual cooperation between belligerents, who comply only with those rules that serve their joint interests. For example, a belligerent might believe that it gains an advantage by executing POWs—but not if the other side executes prisoners as well. The best outcome for both sides is to refrain from executing POWs, so both do. States normally expect a war to end in a settlement and peace, and they do better by reaching that goal with limited rather than with maximal destruction. The law of war provides a framework for keeping destruction to a minimum.

Witt is not as clear about where he stands in this debate as he could be. The pragmatic view makes the best sense of his narrative of the Civil War, and he occasionally acknowledges it, but he also argues for the moral-constraint view.  He writes, “If the law of war were nothing but the condensed interests of particular constituencies at particular moments, it would not do the work that so many have invested in it.” But the law of war can serve the interests of particular constituencies at particular moments and “work” to the extent that constituencies on both sides of a war have interests that converge. This happens from time to time—during World War II, countries refrained from using chemical weapons both because they feared retaliation and were uncertain as to its practical value.

In the end, only the pragmatic understanding of the law of war avoids a supposed paradox that Witt makes much of: If the goal of the war justifies the deaths of hundreds of thousands of one’s own soldiers, why doesn’t it also justify a few law of war violations that improve your chances of victory? Witt, citing President Obama, argues that a country must approach war with humility about its war aims, recognizing that they could be false and therefore harsh means could be unjustified. But this makes little sense from the standpoint of moral psychology or politics. The pragmatic view holds that complying with the law of war does not diminish the probability of prevailing in war. If it doesn’t diminish your chances of winning, while at the same time minimizing destruction for both sides on the way to an eventual settlement, the law of war is not inconsistent with a call to national sacrifice.

Still, if some of the conclusions Witt draws are muddled—he has a weakness for adverting to abstractions, like his repeated claim that the Lieber Code balances “justice with humility,” at just those points when precision is demanded—this book will please Civil War buffs, legal and military historians, and international lawyers alike. Witt’s research on letters, drafts, and other documents written by Lieber and the other major figures is impressive, and he presents it lucidly, fairly, and comprehensively, enabling the reader to draw his own conclusions.

The only weak portion of the book is the epilogue, where Lincoln’s saintly aura finally defeats Witt, and the Lieber Code ends up being a Monument to Human Progress, another gift to humanity handed down to us from the Great Emancipator. This is a questionable judgment at best in light of the extraordinary depredations that would take place during the wars of the 20th century.

Moreover, as Sherman pointed out and even Lieber recognized, the morality of the law of war is contestable on its own terms. As Witt himself notes before he reaches the book’s peroration, the problem with “humanizing” war with law is that a “humane” war may be one that is easier to start and harder to stop, and thus in the long term more devastating than an “inhumane” war. Sherman and even Lieber on occasion advocated “short and sharp wars” (184)—where the devastation is so extreme that people will not want to repeat the experience, and so in the long term fewer people die than if war is regulated. (The development of drone technology portends greater military conflict in the future because it permits military engagement at minimal human cost to the belligerent even as it inflicts destruction on its human targets.)

By contrast, during the Cold War both the United States and the Soviet Union threatened to hurl nuclear bombs at each other’s cities if attacked. Incinerating millions of innocent civilians is as obvious a law of war violation as there could be. If the threat of mutually assured destruction kept the peace for so long, what are we to make of the rules that supposedly prohibit it?