How did economic interests tie northerners to the slaveholding system of the South?

Northerners were tied to the slaveholding system of the South in many ways. First, southern plantations supplied the cotton that kept the textile mills of the Northeast running. Thus slavery was a very important part of the rise of industry in the United States (and Great Britain.) Less obviously, Northern companies had a considerable amount of money invested in slavery, and in economic pursuits related to slavery. Insurance companies, for example, insured cotton crops and in many cases, enslaved people themselves. The banks that supplied the capital for the expansion of slavery into the old Southwest and the Mississippi River Valley in the nineteenth century were mostly Northern, and they profited heavily, if indirectly, from slavery. Earlier, the merchant companies that essentially controlled the slave trade before it was outlawed in 1808 were almost exclusively Northern. So, as many historians have shown, the economy of the entire United States was, for much of its history, implicated in slavery.