“In early 1862, George McClellan, then general in chief of the army and a vocal opponent of a war against slavery, gave extremely conservative instructions regarding military emancipation to General Ambrose Burnside as he was about to embark on another joint army-navy operation aimed at capturing Roanoke Island:
” ‘[Say] as little as possible about politics or the negro. Merely state that the true issue for which we are fighting is the preservation of the Union and upholding the laws of the General Government….’
“Upon capturing Roanoke Island in early February, Burnside [denied intending] ‘to liberate your slaves.’ McClellan’s instructions, like Burnside’s proclamations, were technically correct: The ‘purpose’ of the Union invasion was the restoration of the Union, not the liberation of slaves. The policy of the federal government, however, was to emancipate all slaves coming within Union lines…. Occupation forces would not actively interfere with the peaceful operation of slavery among loyal farmers and planters, [or] entice slaves away from their owners, but slaves escaping to Union lines were emancipated and employed as wage laborers.
“Slavery deteriorated rapidly in the occupied parts of North Carolina thanks to the policy instructing Union forces to employ fugitives entering their lines, coupled with the prohibition against military enforcement of the fugitive slave clause.”
– From “Freedom National: The Destruction of Slavery in the United States, 1861-1865″ by James Oakes (2012)