Re. the relationship of capitalism to slavery: as of 1860 slaves (as productive 'property': capital) represented as much value as all of the other capital assets in the country combined. (I learned that via an interview I heard on the radio, so I don't have a reference, but sceptics can look it up.)

The plantations were, not surprisingly, hugely profitable. International sales from the plantation economy accounted for almost all of the specie (money in the form of gold and silver coins) in the nation prior to the discoveries of vast deposits of those metals in western areas of the continent.

Most of those international transactions took the form of exchanges of paper (mostly bills of exchange and notes drawn on banks), without actual money changing hands. Most of that was handled, very profitably, by northern banks where the domestic shipping business was concentrated.

One way and the other, profits from slavery accounted for almost all of the liquid capital that funded the establishment of capitalism as a productive process in the domestic economy. So, yes, capitalism did depend on slavery for its establishment in this nation.

The Civil War was all about eliminating the land-based aristocracy (in turn based on slavery) as the political competitor of a monetary-based plutocracy--which ensued after that war when capitalists effectively purchased all national and state(/territory)-level government in this nation.