... as an economic sanction well into the war, Lincoln outlawed slavery.
Expanding on this --
It's important to note that the Emancipation Proclamation freed slaves only in Confederate-controlled states, and not in Union border states, as well as welcoming any of those freed people into the Union Army. This served the multiple purposes of: creating chaos in the Confederacy; negatively impacting the economy of the Confederacy; forcing states in rebellion to expend more resources on controlling the enslaved people within their borders (and by extension, fewer resources on waging war); and increasing membership in the Union Army.
Seen it in the Caribbean, I expect it's plenty common in places where the sun is a deadly laser.