Final answer:
Tobacco was the most valuable cash crop in the Southern colonies until cotton overtook it following the War of 1812 and especially after Eli Whitney's invention of the cotton gin in 1793. By the mid-19th century, cotton became the predominant cash crop, dominating the southern economy until the Civil War.
Step-by-step explanation:
Tobacco was once the most valuable cash crop in the Southern colonies due to its immense popularity in England and Europe. However, the scenery of agriculture in the South changed significantly after the invention of the cotton gin in 1793 by Eli Whitney, which made the processing of cotton much more efficient. With this revolutionary advancement, and the subsequent cotton boom following the War of 1812, by the midcentury, cotton became the key cash crop of the southern economy and eclipsed tobacco in economic importance. Indeed, by 1860, cotton was king, with the South producing two-thirds of the world's supply and relying heavily on enslaved labor. This established cotton as the most important American commodity, replacing tobacco in its reign over the Southern colonies' economy until it was disrupted by the Civil War.