Final answer:
Cotton was the most influential crop in transforming the southern economy during the antebellum period. The South produced a significant portion of the world's cotton, and its profitability was dependent on slavery.
Step-by-step explanation:
The crop that was most influential in transforming the southern economy during the antebellum period was cotton. By 1860, the South was producing two-thirds of the world's cotton, and American cotton made up two-thirds of the global supply. The profitability of cotton relied on the institution of slavery, which provided the cheap labor needed for its production.
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