"The time has come now," Abraham Lincoln told his cabinet as he presented the preliminary draft of a "Proclamation of Emancipation." Lincoln's effort to end slavery has been controversial from its inception-when it was denounced by some as an unconstitutional usurpation and by others as an inadequate half-measure-up to the present, as historians have discounted its import and impact. At the sesquicentennial of the Emancipation Proclamation, Louis...