Lincoln announced the Preliminary Emancipation Proclamation, which stated that all slaves in rebellious parts of the South on January 1, 1863, would be freed. The President hoped that emancipation would undermine the Confederacy from within. Secretary of the Navy Gideon Welles reported that the President told him that freeing the slaves was “a military necessity, absolutely essential to the preservation of the Union. . . . The slaves [are] undeniably an element of strength to those who [have] their service, and we must decide...