While the Slaves worked and suffered constantly in poor living conditions constant beating's death, starvation, from the south extreme. Slave's that were freed in the north even still had to deal with racism as a free man, The main issue is that Slave's need to eat, dress, and the north supplied that. so while not in blunt force of slavery's riches the north still profits off the south while making goods for slave's and the owners.
Some off the ways the north was profiting off the cotton craze was buying cotton milling into clothing or cloth for the slaves, One of the most common piece of clothing today has roots in this cotton,In the north Cotton mills were making "negro cloth" which was used in many clothes such as jeans mill in new jersey would sell to the slave owners to cloth the slaves.
RIchest of all were the slave owners, this led was literal blood money,with harsh living condition vs this nice house that appears here, the only victor was the owner, no lifestyle of slavery. The north could make close to the slave owner money by using this southern blood and then using the north as an excuse, till the north fought in the civil war is when the north was truly helpful.