Slavery, which was at the core of the North-South split leading to the Civil War, was strangely dismissd as a cause of the war by both sides as hostilities began in 1861. Historian James McPherson wrote in his comprehensive 1988 Civil War history, Battle Cry of Freedom: The Civil War Era, that Abraham Lincoln himself, speaking to Congress in a special session that year, said that he had "no purpose, directly or indirectly, to interfere with slavery in the states where it exists."
Both the North and the South had their reasons for avoiding the issue. McPherson wrote further: "A concern for northern unity underlay this decision to keep a low profile on the slavery issue. Lincoln had won less than half of the popular vote in the Union states (including the border states) in 1860. Some of those who had voted for him, as well as all who had voted for his opponents, would have refused to countenance an antislavery war in 1861. By the same token, an explicit avowal that the defense of slavery was a primary Confederate war aim might have proven more divisive than unifying in the South. Both sides, therefore, shoved slavery under the rug and they concentrrated their energies on mobilizing eager citizen soldiers and devising strategies to use them."