Answer:
A. economic differences in the North and South
Step-by-step explanation:
The economy of the Northern part of United States is dependent on industrialization, where by manufacturing and production of goods is the main point of the economy activities. Its economy favoured tariffs and which protects the factory owners and workers from competition.
On the other hand, the economy of the Southern part of United States is dependent on agriculture, where by, they relied heavily on the enslaved labour force, to work on their plantation farms, because it is cheaper to maintain.
Hence, due to the economic differences in the North and South, some states (southern states) allowed slavery, while others (northern States) did not.