Yet, the Constitution of the new republic assiduously avoided any explicit mention of slavery, and the authors of the Constitution routinely deplored it. Washington freed his slaves in his will; Franklin became the president of the Pennsylvania Abolition Society. "All men are, white or black … by the law of nature freeborn," declared James Otis. The laws of economics, however, dictated otherwise. Especially after Americans discovered the enormous profits to be reaped from cotton, the demand for a cheap labor force spawned a new intellectual industry: the manufacture of excuses for perpetuating slave labor, especially in the fertile cotton-growing states of the South; and this industry, allied with all the irrational fury of racism, justified the imposition of slavery on blacks. Thus emerged the great American political hypocrisy—a republic of liberty prospering on the backs and sweat of slave labor.

Abraham Lincoln did not think of himself as a redeemer, but he became the redeemer of the American purpose as the man who finally overthrew slavery. Not just the noxious institution, but the entire principle of a human labor force born only to labor. "I am naturally anti-slavery," he remarked in 1864, "If slavery is not wrong, nothing is wrong. I can not remember when I did not so think, and feel." That revulsion began in Lincoln’s mind with the way slavery made working men ashamed of laboring with their hands, because manual labor was "slave work." Owning slaves "betokened not only the possession of wealth but indicated the gentleman of leisure who was above and scorned labour." He hated it, too, because of the laughter it provoked at American pretensions from aristocrats and dictators around the world. Americans were "proclaiming ourselves political hypocrites before the world, by thus fostering Human Slavery and proclaiming ourselves, at the same time, the sole friends of Human Freedom." Above all, slavery violated the natural rights to life, liberty, and the pursuit of happiness that were hard-wired into human nature by its Creator. "The ant, who has toiled and dragged a crumb to his nest, will furiously defend the fruit of his labor, against whatever robber assails him," Lincoln wrote, and in just the same way, "the most dumb and stupid slave that ever toiled for a master, does constantly know that he is wronged."

At the same time, though, Lincoln was aware that there was more than one way to wreck the republic. Ignoring the ideological cancer of slavery was one way; but taking up a cudgel, as many abolitionists urged, would be just as destructive. Slavery was an "interest" which controlled the politics of the southernmost tier of the United States, and the slaveholding states angrily threatened disunion every time an unfriendly move was made against slavery. Lincoln hoped that the best long-term solution would be to contain slavery in the Southern states where it had long been legalized. "I hold it to be a paramount duty of us in the free states, due to the Union of the states, and perhaps to liberty itself (paradox though it may seem) to let the slavery of the other states alone," Lincoln explained in 1845, "while, on the other hand, I hold it to be equally clear, that we should never knowingly lend ourselves directly or indirectly, to prevent that slavery from dying a natural death—to find new places for it to live in, when it can no longer exist in the old." But by the 1850s, new places—in the undeveloped western territories—were exactly what the "Slave Power" was demanding. And when Lincoln was elected president in 1860, they regarded his policy of non-extension as being as good as a declaration of war, and eleven of the slave states promptly announced their secession from the United States to form a slave republic, the Confederate States of America. Unilateral secession, Lincoln announced, was unconstitutional, and nothing better than a fancy word for rebellion. And so the great American Civil War began.

Lincoln understood, even as he took the oath to become president in the spring of 1861, that he had no authority to lay hands on the state laws that had legalized slavery. Even when the Southern states seceded anyway, he kept on insisting that his responsibility as president extended only as far as suppressing secession and restoring the federal Union, not abolishing slavery. But Lincoln also knew that the Civil War was bound to have a disruptive effect on slavery. And he also knew that there were indirect ways to undermine slavery. Which is why, little more than six months after taking office, Lincoln devised a federal buy-out plan (intended for the four slave-holding states which had not joined the Confederacy) which would induce the state legislatures to purchase the freedom of slaves from their owners. He also signed legislation to abolish slavery in the District of Columbia (the one place where the federal government did have direct authority). And he sanctioned the use of runaway slaves as government laborers, and then as soldiers in the Union army.

But this only nibbled at the edges of slavery. Finally, in the summer of 1862, he struck out on a new path. Relying on the argument that the Confederacy’s slaves constituted a significant military asset to the rebels, and on the constitutional argument that, as commander-in-chief, he had the authority to seize and emancipate slaves "as a war measure," Lincoln drafted a "war powers" proclamation which declared the Confederacy’s slaves "thenceforward, and forever free." He read a first draft to his cabinet in July, released a preliminary version in September, and then a final—and enforceable—proclamation on January 1, 1863. "And upon this act," he added at the end, "sincerely believed to be an act of justice, warranted by the Constitution, upon military necessity, I invoke the considerate judgment of mankind, and the gracious favor of Almighty God."

The Emancipation Proclamation was a cautious and legalistic document, strangely removed from the eloquence that graced so many of Lincoln’s other speeches and letters. But Lincoln had always to keep in mind how easily an uncooperative judiciary could undo his proclamation. And in fact, it worked. The Emancipation Proclamation declared legally free over 3 million slaves, and over the course of the Civil War, over 200,000 of those slaves were liberated—not just seized or confiscated, but actually set irretrievably free—by the advance of the Union armies.

It was not his final act of emancipation, however. More than just emancipating slaves, Lincoln wanted the entire principle of slavery erased from the American escutcheon, and so in 1864, he called for a thirteenth amendment to the Constitution, which outlawed slavery everywhere in the United States. But this was only the final burial of the injustice. Its death sentence was the Emancipation Proclamation, and Lincoln confidently described it as "my greatest and most enduring contribution to the history of the war," and "as affairs have turned, it is the central act of my administration, and the great event of the nineteenth century."

Allen C. Guelzo is Henry R. Luce Professor of the CivilWar Era, Director of CivilWar Era Studies, and Associate Director of the Civil War Institute at Gettysburg College in Gettysburg, Pennsylvania.