Im just saying that you can see the influence there Civil War had on Marx's later works. He realized that American slaves had much more in common with the proletariat than he previously saw (tacit abandonment of the concept of lumpenproletariat).

He also saw that the working classes of both America and England were capable of understanding longer term goals that may be immediately harmful to them (striking to prevent the supply of raw material from a slave source).

It has been a while since I've read the book though, so I'm a bit rusty. I just know that you get to see a lot of his internal thought processes hitting points that were later adopted by ML leaders.