Final answer:
Nat Turner led an 1831 uprising in Southampton County, Virginia, which was the most frightening event for white southerners in the antebellum period.
Step-by-step explanation:
The most frightening event for white southerners in the antebellum period was the 1831 uprising led by Nat Turner in Southampton County, Virginia. Nat Turner, an enslaved man, was inspired by evangelical Protestantism and believed he was chosen to end slavery.
He organized other enslaved people and carried out a rebellion, resulting in the killing of numerous white individuals. The rebellion was a significant event in American history and led to stricter laws and restrictions on enslaved individuals.