One hundred and forty years ago today, the Emancipation Proclamation struck the shackles from 4 million African American slaves. It was the single most revolutionary document in our history after the Declaration of Independence.

And yet, although Abraham Lincoln saw the Proclamation as "the central act" of his administration, it is given little attention today when compared with Lincoln's other famous state papers: the Gettysburg Address, the Second Inaugural, the Bixby letter. Certainly one reason for the Proclamation's modest visibility is the modesty of its language. The Gettysburg Address soars with eloquence; the Second Inaugural closes with the profound gentleness of a benediction. The Emancipation Proclamation is plain and flat, bristling with "whereases" and "therefores" and "aforesaids." It reads, in other words, like a lawyer's brief, and it made Karl Marx (who was then eking out a living as a journalist in London) think of a summons sent by one country attorney to another. As historian Richard Hofstadter wrote, the Proclamation "has all the moral grandeur of a bill of lading."

There is some truth to this. The Emancipation Proclamation, all of 622 words, merely announces that it is fulfilling the promise Lincoln had made a hundred days earlier, on Sept. 22, 1862, to use his war powers as president to free the slaves. It warns the newly freed slaves "to abstain from all violence, unless in necessary self-defence." And it adds that these slaves will also be accepted for enlistment in the previously all-white Union army. Not a word about citizenship. Not a word about civil rights. And all of it is based, not on justice or truth, but on "military necessity."

Over the years, it has become fashionable to take the legal blandness of the Proclamation as proof that Lincoln's heart was not in it, or that he resorted to freeing the slaves only when every other tool to win the Civil War had broken in his hand. But taking a step backward allows us to see just how cranky those criticisms really are. Lincoln was a skillful politician, but he was not a cynic, and especially not about slavery. "I have always hated slavery," Lincoln once said. "If slavery is not wrong, nothing is wrong." From his first months in office, he worked to undermine slavery by offering a federally financed buyout to slave owners in the four slave states that remained in the Union. When his own generals looked as if they might waver politically over fighting to free black slaves, Lincoln bolted ahead to use his constitutional power as commander in chief to free the slaves by proclamation.

If the language of the Proclamation sounded flat and legalistic, there was good reason. The use of presidential "war powers" has long been a sore point in constitutional theory. And once a wartime emergency ended, anything a president did on the strength of the "war powers" would inevitably be challenged in federal court, and possibly overturned. Strange as it may seem, bitter-end slaveowners had every prospect, even after military defeat, of appealing any emancipation edict of Lincoln's all the way up to the Supreme Court. And the chief justice of the court was Roger Brooke Taney, the same chief justice who had written the majority opinion in the infamous Dred Scott case (which denied that blacks could be citizens). Taney had tried to strangle the Union war effort at the very beginning in ex parte Merryman (making arrests of Confederate agents impossible), and was, in 1863, trying to have the Union blockade of Confederate ports declared unconstitutional. If the Proclamation hadn't been written in the strictest, flattest, most precise legalese, Taney and the court would have picked it to pieces, and the cause of black freedom would have been set back again.

True, there was no promise of black voting rights or education, no pledge of equal citizenship. But in those days before the 14th and 15th Amendments, voting rights, education and even citizenship were all matters handled by the states. A constitutional firewall blocked the federal government's jurisdiction in those matters, and any attempt by Lincoln to leap over it would only put the cause of black freedom in greater legal jeopardy. As it was, Lincoln turned the screws as hard as he dared on Union occupation forces to nudge the reconstruction of the South toward voting rights and education. And he shut down any attempt at postwar litigation against emancipation by pushing through Congress a 13th Amendment to the Constitution abolishing slavery throughout the nation.

If anything, we underestimate the political courage it took for Lincoln to issue the Emancipation Proclamation and then stand behind it. Six weeks after he gave his hundred-days' warning, the midterm congressional elections dumped 45 Republicans from their seats in the House of Representatives.

The Union army smoldered with rumors of mutiny and coup. Two state legislatures -- Illinois and Indiana -- were so violent in their condemnation of the Proclamation that they had to be closed down by their governors. And in July 1863, New York City erupted in a riot over the draft that quickly turned into a bloody anti-emancipation carnival.

Blacks did many things for themselves to throw off the yoke of slavery. More than 180,000 fought in the Union army. But in the end, it might easily have come to nothing without Lincoln and the Emancipation Proclamation. If the Proclamation sounds to us too much like a "bill of lading," we should remember that it was for a cargo of 4 million people, bound for the shores of freedom.

The writer is a James Madison Fellow in the Department of Politics at Princeton University.