The code reduced the international laws of war into a simple pamphlet for wide distribution to the amateur soldiers of the Union army. It prohibited torture, poisons, wanton destruction, and cruelty. It protected prisoners and forbade assassinations. It announced a sharp distinction between soldiers and noncombatants. And it forbade attacks motivated by revenge and the infliction of suffering for its own sake. Most significantly, the code sought to protect channels of communication between warring armies. And it elevated the truce flag to a level of sacred honor.
In the spring of 1863, Lincoln's code was given not just to the armies of the Union but to the armies of the Confederacy. The code set out the rules the Union would follow—and that the Union would expect the South to follow, too. For the next two years, prisoner-exchange negotiations relied on the code to set the rules for identifying those who were entitled to prisoner-of-war status. Trials of Southern guerilla fighters and other violators of the laws of war leaned on the code's rules for support. The Union war effort became far more aggressive than it had been under McClellan's rules. As the Union's fierce Gen. William Tecumseh Sherman put it, Lincoln brought the "hard hand of war" to the population of the South. But this more aggressive posture was not at odds with Lincoln's new code. It was the code's fulfillment.
As the code's Confederate critics noticed immediately, the laws of war Lincoln announced in 1863 were far tougher than the humanitarian rules McClellan had demanded a year earlier. The code allowed for the destruction of civilian property, the bombardment of civilians in besieged cities, the starving of noncombatants, and the emancipation of civilians' slaves. It permitted executing prisoners in cases of necessity or as retaliation. It condoned the summary executions of enemy guerillas. And in its most open-ended provision, the code authorized any measure necessary to secure the ends of war and defend the country. "To save the country," the code declared, "is paramount to all other considerations." Lincoln's code was a body of rules not for McClellan's gentleman's war but for Sherman's March to the Sea.
In the decades after the Civil War, Lincoln's rules went global. International norms become international law only when great powers agree to comply with them, and Lincoln's code seemed to allow the great powers of the world to prosecute war aggressively without descending into wars of total destruction. Translations of the code spread through the armies of Prussia and France and into multinational treaties signed at The Hague. Following World War II, its provisions reappeared in the Geneva Conventions that are in effect to this day. Eventually, Lincoln's code would make its way into the pockets of men and women stationed around the world, in the field manuals and wallet cards that soldiers carry with guidelines for the laws of armed conflict.
Yet if soldiers still today carry around a little bit of Old Abe Lincoln in their pockets, the appeal of his approach to the laws of war has waned in recent decades. Today, the two leading paradigms for the laws of war are a humanitarian model and a war crimes model. The former would base the laws of war in individual human rights, the latter in the criminal tribunals like the one at Nuremberg after World War II.
In 1862 and 1863, Lincoln was up to something very different. His personal passage from law-of-war skeptic to law-of-war reviser in the midst of the Civil War offered him a distinctive vantage point. His code sought to organize the laws of war not around individual human rights or war crimes trials, but around reciprocity and coordination between armies. Lincoln's code set limits on his army's conduct, to be sure. But it also aimed to win a war. The function of Lincoln's laws of war was thus to identify and protect opportunities for cooperative behavior even in the clash of armed conflict.
In our own time, Lincoln's pragmatic model of the laws of war can help us in Iraq and Afghanistan. There is little prospect of reciprocity with terrorists, of course. But if one thing has become apparent in the cross-border security threats of the 21st century, it's that cooperation among the decent states of the world will be indispensable to policing against common threats. This is what Secretary of State Hillary Clinton meant when she stated in her confirmation hearings, "Today's security threats cannot be addressed in isolation." Combating terror, according to Clinton, requires "reaching out to both friends and adversaries, to bolster old alliances and to forge new ones." Lincoln's laws of war did just that. They were ways of reaching out to bolster cooperation even in the midst of conflict.
For the past seven years, America has repeated the journey Lincoln completed in 24 grueling months. Strong majorities of Americans now call for the dismantling of detention facilities at Guantanamo. Even stronger majorities oppose the use of torture in interrogations. As a nation, we have walked in Lincoln's footsteps, down an uncertain path from skepticism about the laws of war to a rediscovery of their pragmatic mix of toughness and humanity. President Obama, in his inaugural address, pledged to reconcile our interests and our ideals. This is precisely what Lincoln's laws of war sought to accomplish, rejecting lawlessness while relentlessly pursuing threats to our way of life.