Walter Johnson, in The New York Times:
Every year, British merchant banks advanced millions of pounds to American planters in anticipation of the sale of the cotton crop. Planters then traded credit in pounds for the goods they needed to get through the year, many of them produced in the North. “From the rattle with which the nurse tickles the ear of the child born in the South, to the shroud that covers the cold form of the dead, everything comes to us from the North,” said one Southerner.As slaveholders supplied themselves (and, much more meanly, their slaves) with Northern goods, the credit originally advanced against cotton made its way north, into the hands of New York and New England merchants who used it to purchase British goods. Thus were Indian land, African-American labor, Atlantic finance and British industry synthesized into racial domination, profit and economic development on a national and a global scale.
It is not simply that the labor of enslaved people underwrote 19th-century capitalism. Enslaved people were the capital: four million people worth at least $3 billion in 1860, which was more than all the capital invested in railroads and factories in the United States combined. Seen in this light, the conventional distinction between slavery and capitalism fades into meaninglessness.