The north had no need for the commodity, the buying and selling and propagation of slaves.
Look at some types of commodities currently addressed as a financial activity on the stock market...
The way slaves were marketed yesteryear seemed goofy to the North and to us today...imagine what some in the world think of trading pork bellies on the open market...
but then only NITWITS believe the war was about slavery. it was about FREEDOM for dixie. (or "preserving the union", if you're a bluecoat apologist)
free dixie,sw