As Abraham Lincoln addressed the nation at his Second Inaugural on March 4, 1865, almost 100,000 slaves in the border states loyal to the Union enjoyed freedom for the first time. All were women and children, emancipated on that day by an act of Congress designed to encourage enlistments by black men in the Union army.

Meanwhile, on the steps of the Capitol, the president spoke of the Civil War as punishment for the sins of slavery, intoning “Woe unto the world” but envisioning peace, “with malice toward none.”

Unlike Lincoln’s words, the Enlistment Act has been forgotten. It has no place in most histories of slave emancipation and has disappeared from public memory. No monuments exist to mark it. But this moment of wartime liberation was a turning point in the downfall of American slavery, one in which slaves played a leading part in transforming the Civil War into a war for abolition.