Not surprisingly, the northern textile mills did just fine without the "cheap cotton extorted from the south".
They raped the south and its people. They distorted the cause of the war to be about slavery. Just fine is not how I would describe it.
The very same people ran the slave trade and who ran their slave markets right there in Boston blamed the South for slavery. There was a slave market right in Faneuil Hall. Ironically it is part of the Freedom Trial.