Final answer:
The dramatic increase in the South's slave labor force between 1810 and 1860 was primarily due to the natural population increase of American-born slaves.
Step-by-step explanation:
The dramatic increase in the South's slave labor force between 1810 and 1860 was primarily due to the natural population increase of American-born slaves. As the enslaved population in the South grew, there was less need for importing new slaves from other regions. Additionally, the banning of the international slave trade in 1808 limited the supply of enslaved Africans from the African slave trade. Although the acquisition of Louisiana expanded the territory of the South, it did not significantly contribute to the increase in the slave labor force. The severity of fugitive slave laws and the importation of slaves from the West Indies were not the main factors driving the dramatic increase in the South's slave labor force during this period.
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