In August 1863, eight months after Lincoln issued the Emancipation Proclamation, he responded to an invitation from Illinois State Agent James Conkling to attend a rally in Springfield, Illinois, to support the Union cause in the Civil War. He expressed regrets over his inability to travel from Washington, D.C., to attend, and, more important, he explained his rationale both for the continued conduct of the war and for his presidential directive declaring all slaves in the Confederacy free from that point forward. Lincoln used the letter to make two central arguments: one defending the use of military force by the Union against the Confederate States of America and a second addressing the centrality of the issue of slavery to justify the war.