That Time This Union Officer Regretfully Declined To Send Back These Fugitive Slaves
https://www.wonkette.com/p/that-time-this-union-officer-regretfully
Erik Loomis - Wonkette

Another good history lesson to go along with Heather Cox Richardson's.
On May 23, 1861, three slaves named Shepard Mallory, James Baker, and Frank Townsend fled to Fort Monroe, Virginia, to escape their master. Benjamin Butler, the Massachusetts politician turned officer in command of the fort, declared them contraband and refused to return them. This maneuver satisfied the Lincoln administration, which did want to find a way to undermine slavery but also needed to keep slave states in the Union. It also set the terms by which slave laborers themselves would play a critical role in the Civil War by taking themselves and their labor to Union lines, severely hurting the Confederate war effort.
Slaves wanted freedom from the moment they were forced from Africa. There are many slave rebellions early in American history led by slaves newly arrived from Africa, from New York to South Carolina. With the official end of the transatlantic slave trade by the US in 1807, the number of Africans entering the nation declined (though did not disappear as illegal slave trading continued), but slave rebellions still took place, such as that led by Nat Turner in 1831. Moreover, southern whites freaked out constantly over the prospect of facing a Haiti-like slave rebellion. If only.
War provided slaves opportunities to escape. During both the American Revolution and the War of 1812, slaves fled by the thousands to British lines. The British had not really expected this, even the second time, and so did not necessarily have a strategy to deal with it. Then they told the British how to attack their masters and served as guides through the swampy waterways to both burn the plantations and free their fellow slaves. The British quickly realized the effectiveness of this strategy and began promising slaves freedom to escape. These promises were followed up with half-hearted results at best, but still, it was a pathway for freedom for thousands of people.
The Civil War was a different type of conflict in these early years, largely because while southern whites, northern African-Americans, and enslaved people all knew what the war was about, northern whites were highly unsure and thus did not take on the enemy as they should have. This could lead to all sorts of issues -- think of George McClellan commanding Union forces while thinking Lincoln was just as much a threat to the future of the nation as any Confederate. It also led to a lack of clear focus on the slave labor issue. Slaves themselves changed that focus.
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