Today marks the 150th anniversary of President Abraham Lincoln’s most extreme military order as commander in chief: the “Order of Retaliation” of July 30, 1863.

Less noted and remembered—and certainly less celebrated—than Lincoln’s more famous military order, the Emancipation Proclamation, the Order of Retaliation shares with it a key feature: they both rested on the president’s constitutional military authority.

Yet while the Emancipation Proclamation memorably declared slaves free, the Order of Retaliation ordered the intentional killing of captured Confederate prisoners of war, in retaliation for the South’s atrocities against black Union troops: Confederate policy was to take no black prisoners. Captured black Union soldiers were either enslaved (or re-enslaved), or simply killed on the spot.

Lincoln styled his Emancipation Proclamation as an “act of justice, warranted by the Constitution, upon military necessity.” And it certainly was that. Was the Order of Retaliation likewise “an act of justice”? Was it a regrettable, but necessary, war measure to protect black soldiers from re-enslavement or brutal massacre? Or was Lincoln’s order itself a war crime, or a threat to commit one, and a moral atrocity in its own right? However we answer this question, we are left with practical, constitutional, and moral implications for the scope of presidential military power today.

The Emancipation Proclamation and the Order of Retaliation

The Emancipation Proclamation, first issued in September 1862 (Lincoln made it final on January 1, 1863), proclaimed “forever free” all slaves held in Confederate-controlled territory. Constitutionally, the proclamation was justified solely as a presidential military measure authorized by the customary law of war. Lincoln lacked any other constitutional power to declare slavery abolished—a president cannot make law by decree—and it was thought doubtful whether Congress had such power either.

So, legally speaking, Lincoln was not enacting a national law of emancipation. He was simply ordering Union troops to confiscate an enemy resource and turn it to Union advantage in time of war.

That was why the Emancipation Proclamation did not (and could not) extend to the four slave states that had remained in the Union. It is also why Lincoln worried that the Proclamation might not remain legally operative after the war, which is part of the reason he pressed hard for passage of the Thirteenth Amendment, abolishing slavery, early in 1865—before the war concluded and the status of emancipated blacks might be thrown into doubt.

But the Proclamation did more than simply declare Southern slaves free. Lincoln also stipulated that more than 180,000 free black men and former slaves would be “received into the armed services of the United States” to fight in the ranks of the Union army and navy.

This was an act of enormous consequence in its own right. Emancipation of slaves was one thing. Enrollment of former slaves into Union armed forces, to fight against their former masters, was something else. It was an assault on the Confederacy’s most fundamental premises: white superiority, the sanctity of the right to slave property, and the illegitimacy of government interference with the “domestic institutions” of the states. Lincoln now proposed to turn those premises on their head and use Southern slaves as an instrument of the Union’s war against their masters.

Southerners practically went berserk with rage. They considered Lincoln’s act of enrolling black troops a moral outrage—the fomenting of slave insurrections (a capital crime in the South) and the use of “savages” to war against them (a war crime in the South’s view of things).

Confederate President Jefferson Davis condemned Lincoln’s arming of black men, whom Davis deemed “human beings of an inferior order,” as calculated to produce “the most execrable massacre recorded in the history of guilty man.” After the proclamation, Davis directed Confederate soldiers not to treat captured Union black troops as prisoners of war. Instead, they were to be enslaved or executed. Their white officers, if captured, were to be tried and executed as the lowest of criminals.

In May 1863, the Confederate Congress formalized Davis’s policy, providing for military proceedings and executions instead of state prosecutions. In the infamous words of Confederate Secretary of War James Seddon, the South’s policy was “never to be inconvenienced with such prisoners . . . summary execution must therefore be inflicted on those taken.” And the South acted on this policy: on several occasions in 1863 and 1864, hundreds upon hundreds of black Union soldiers were deliberately massacred after surrendering. Thousands more were enslaved.

Lincoln answered Davis and the Confederate Congress with his July 30, 1863, Order of Retaliation. “It is the duty of every government to give protection to its citizens, of whatever class, color, or condition, and especially to those who are duly organized as soldiers in the public service,” he began. The laws and customs of war “permit no distinction as to color in the treatment of prisoners of war as public enemies. To sell or enslave any captured person, on account of his color, and for no offence against the laws of war, is a relapse into barbarism and a crime against the civilization of the age.”

The United States would protect its soldiers, black and white. Therefore, if the enemy “shall sell or enslave anyone because of his color, the offense shall be punished by retaliation upon the enemy’s prisoners in our possession.” Lincoln specified the form such retaliation would take:

It is therefore ordered that for every soldier of the United States killed in violation of the laws of war, a rebel soldier shall be executed; and for every one enslaved by the enemy or sold into slavery, a rebel soldier shall be placed at hard labor on the public works and continued at such labor until the other shall be released and receive the treatment due to a prisoner of war.

This was extraordinary. Lincoln had authorized, by presidential military command, the deliberate killing of captured Confederate soldiers who themselves had committed no crime against the laws of war. Such killing was, moreover, explicitly denominated an act of retaliation directed against innocent men. Soldiers who had surrendered, laid down arms, and been taken into custody as prisoners, were now to be killed for sins of their brothers in which they had taken no active part.

Lincoln’s Moral Reservations: From Retaliation to Deterrence

Lincoln’s order, had it been enforced, would not have been entirely unprecedented in the annals of modern warfare. But today it would be regarded as itself a violation of the international laws of war—a grave breach of the Geneva Conventions regarding treatment of prisoners of war.

The Order of Retaliation was never carried out, largely due to Lincoln’s own moral reservations about it and his practical judgment that doing so would produce more harm than good. As he explained to the former slave and forceful advocate for blacks, Frederick Douglass, executing Confederate prisoners would probably only prompt the South to kill other Union prisoners.

Yet Lincoln was sorely tested on this point. The South deliberately massacred surrendered black Union troops several times in the year following Lincoln’s order: at Fort Pillow (Tennessee), Poison Springs (Arkansas), Plymouth (North Carolina), and Olustee (Florida).

The Fort Pillow massacre, in April 1864, was the most infamous incident. Confederate cavalry commanded by Nathan Bedford Forrest slaughtered hundreds of black Union soldiers after they had lain down arms. Reports reached Washington quickly, and an investigation soon confirmed the worst. Lincoln’s cabinet deliberated about the right response, splitting down the middle between those who favored retaliatory executions and those who, with Lincoln, thought doing so would be futile, morally dubious, and simply produce a cycle of retaliation.

In the end, on May 17, 1864, Lincoln directed his Secretary of War to identify and set aside, by name, explicitly as “hostages,” some 300 Confederate officers, a number equaling those massacred at Fort Pillow. The Secretary of War was further to communicate to rebel forces the Union’s determination that an unlawful massacre had occurred at Fort Pillow, that these captured men (all officers) had been set aside as a result, and that they would not be executed if no further such acts took place and if the Union received assurance that no Union soldiers—“whether white or colored”—would be treated “other than according to the laws of war.”

The clear but unstated implication was that the marked men would be executed if there were further massacres, or if the necessary assurance was not received. Lincoln had subtly shifted his policy from one of retaliation to one of deterrence.

There is no record of the South ever sending any formal notification of compliance with Lincoln’s condition. And Fort Pillow was not the last time during the war when surrendered Union troops were killed.

But Lincoln never killed any hostages. At most, Union commanders, seeing captured black soldiers placed at hard labor on Confederate fortifications under Union fire, returned the favor. They put captured Southern soldiers to work on Union fortifications under Confederate fire. This, apparently, stopped that particular practice.

At the same time, the Union discontinued prisoner exchanges between the two armies unless and until the South agreed to return black soldiers on the same terms as whites. They would not. And so no one was exchanged, leading to the horrors of large prison camps on both sides—but especially in the South, the worst being the Confederate death trap of Andersonville, Georgia, where 13,000 Union troops were left to perish.

Lincoln could have resumed prisoner exchanges, had he been willing to abandon black soldiers, and he took considerable political heat in the North for not doing so. But as General Benjamin Butler, Lincoln’s appointed exchange agent, put it in a widely published letter to the Confederate exchange commissioner: “The wrongs, indignities, and privations suffered by our soldiers would move me to consent to anything to procure their exchange, except to barter away the honor and the faith of the Government of the United States, which has been so solemnly pledged to the colored soldiers in its ranks.”

Late in the war, Union General Ulysses S. Grant and Confederate General Robert E. Lee discussed prisoner exchanges. Grant was willing, as long as black soldiers were included. Lee responded that “property” belonging to citizens of the South was not included in his offer of exchange. Grant cut off the discussion.

Lincoln thus insisted on the principle, and held firmly to it in practice, that black Union soldiers were entitled to equal treatment as prisoners of war. But he did so at great practical cost measured in lives of Union prisoners lost to the barbaric conditions of the South’s camps. And he did not retaliate in kind—he did not kill as he had threatened to do—Southern prisoners held by the North.

Implications for Presidential Military Power Today

Did Lincoln act rightly? Was the Order of Retaliation morally justified in the first instance? Would Lincoln have been justified in carrying it out, as several, including the former slave and great abolitionist advocate Frederick Douglass, apparently urged him to do? Was Lincoln wrong not to do so?

As the late historian William Lee Miller wrote in his magnificent book President Lincoln: “It is to Lincoln’s credit that in the depth of his original righteous indignation he signed this order, and it is also to his credit that in the event—in the scrupulous care of his later reflection—he never carried it out.” That is a wise and thoughtful judgment, but both parts are debatable.

There have been other retaliation orders in the annals of America’s military history, not always to their commanders’ credit. One thing that makes Lincoln’s order singular, or nearly so, was that it was directed against US citizens. For so these prisoners remained, legally, in the eyes of the North. Secession was unconstitutional, Lincoln maintained, and the South’s declared secession was therefore legally ineffective. The South remained in the Union. There was no “Confederacy” (whenever Lincoln used the term, he added the preface “so-called”) but only a massive illegal rebellion by US citizens. That was the whole premise on which the North fought the Civil War.

Lincoln nonetheless thought it legally proper—within his constitutional power as president and commander in chief to wage war—to employ the war power of the United States against US citizens. And in doing so, Lincoln felt it within his moral and constitutional authority to apply his interpretation of the law of war, as it then stood, against citizen-enemy war prisoners.

It is always perilous, and sometimes trite, to try to force history to provide lessons for today. Still, if one judges Lincoln’s actions to be proper, much would seem to follow for today’s controversies. If one considers them improper, that has implications too. If the Order of Retaliation—authorizing the killing of US citizens captured and held as enemy prisoners of war for purposes of retaliation or deterrence, and not for any war crimes personally committed—was morally and legally legitimate, then overseas drone attacks on US citizens engaged in active command of terrorist war crimes by unlawful combatants—the case of Anwar al-Awlaki, killed by drone attack in Yemen in 2011—would seem a fairly easy case by comparison. (Killing al-Awlaki is like a Union soldier shooting at Robert E. Lee.)

If killing an enemy prisoner, to retaliate for enemy atrocities and deter further ones, is even remotely within the realm of moral contemplation as a measure to protect American soldiers’ lives (as Lincoln seems to have thought), then mere “enhanced interrogation” techniques used on enemy war criminals, as a measure to save American lives and causing no permanent injury, begin to seem less troubling. Simple military detention of unlawful enemy combatants abroad, at places like Guantanamo Bay, for as long as hostilities continue, seems positively unproblematic by comparison with Lincoln’s Order.

But if Lincoln acted wrongly—if enemy prisoners cannot be summarily executed in retaliation—the propriety of today’s disputed tactics remains an open question. Lincoln’s order remains an extreme polar case. Deliberate killing of surrendered non-combatants in custody, other than upon conviction for war crimes, is surely worse than targeted drone attacks, coercive interrogation, or indefinite detention. Nevertheless, the underlying moral question—may evil means be employed for a good end?—frames the question of the morality of these disputed tactics today, as it frames nearly all questions of morality in war.

Law, of course, thrives on precedent. Is the Order of Retaliation a precedent for thinking about the constitutional question of the scope of presidential (as opposed to congressional) power to conduct war, and the power to interpret the law of war?

Irrespective of its moral status, if Lincoln’s Order of Retaliation was within the scope of his legal authority to make as Commander in Chief, then one would think most of today’s disputed questions of constitutional presidential war power should be resolved in the same direction: decisions concerning capture, detention, interrogation, and military punishment of enemy prisoners; decisions concerning the proper interpretation and application of the law of war with respect to such subjects (and others); decisions concerning the meaning and force of treaties and other international law with respect to the conduct of war, all would seem to fall within the president’s powers, not Congress’s. That power may be exercised wisely or foolishly, morally or immorally, but it is committed to the president’s judgment.

If the Order of Retaliation was constitutional, then all the more clearly so have been President Obama’s decisions—and President Bush’s before him—concerning war prisoner status, application of international conventions, use of military commissions, extradition and rendition to other countries, and targeted killings of enemy leaders, including Americans. Conversely, if Bush or Obama is to be condemned for any of these acts—there are still a few on the lunatic fringe who continue to label George W. Bush and others in his administration as “war criminals”—how much more strongly must that charge not fall, historically, on the head of Abraham Lincoln?

It is also possible to say that Lincoln’s Order of Retaliation simply is not appropriately considered an historical or legal precedent for anything in particular today. It was simply the desperate, impassioned act of an infuriated but principled president, at the height of war, in the face of enemy atrocities against a particular class or race of American soldiers fighting for their country. In this view, the order bears no particular meaning for anything specific today but is simply an interesting historical event.

Perhaps. But if so, we should at least ponder whether Lincoln’s actions were right or wrong, to identify precisely why, and to appropriate those principles for our public discourse and political ethos today, a century and a half later.

Michael Stokes Paulsen is University Chair and Professor of Law at the University of St. Thomas, in Minneapolis, and author most recently of Our Constitution: Landmark Interpretations of America’s Founding Document (The Federalist Society, 2013). He is working on a book on Lincoln, the Civil War, and the Constitution.