The South based its economy on the use of slaves for agricultural production of things like cotton and tobacco. The North had significant amounts of industry and other finished goods. The South could supply some of the raw materials for the industry of the North. Regardless, the North relied on paid labor.
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Https://www.tamaqua.k12.pa.us/cms/lib07/PA01000119/Centricity/Domain/119/TheAgeofImperialism.pdf