Allen C. Guelzo is the author of Fateful Lightning: A New History of the Civil War and Reconstruction (Oxford University Press, 2012).

Do not look for a great celebration to break out on July 22.

Granted, the 22nd of July has never been much of a red-letter day. No great battles to commemorate, no horrifying cataclysms, no lily-gilding birthdays. The one event that does hang a laurel around July 22 will still go largely unnoticed — despite being at the heart of great battles, a national cataclysm, and a new birth of freedom — and that is Abraham Lincoln’s unveiling of the Emancipation Proclamation to the startled members of his cabinet, exactly 150 years ago this Sunday.

The Emancipation Proclamation did more, and for more Americans, than any other presidential document before or since. It declared that over 3 million black slaves (representing some $3 billion in capital investment) would “thenceforward, and forever, be free” (thus transforming that $3 billion into a net zero, overnight) and turned the Civil War from being a police action against the breakaway southern Confederacy into a crusade for freedom. It was, as Lincoln himself said, “the central act of my administration and the great event of the nineteenth century.”...