Why were southern landowners so wealthy in the mid-1800's

During the antebellum years, wealthy southern planters formed an elite master class that wielded most of the economic and political power of the region. They created their own standards of gentility and honor, defining ideals of southern white manhood and womanhood and shaping the culture of the South. To defend the system of forced labor on which their economic survival and genteel lifestyles depended, elite southerners developed several proslavery arguments that they levied at those who would see the institution dismantled.