Was the southern economy dependent on slavery?

Yes, the southern economy was dependent on slave labor. Rather than industrializing like the northern states, the southern states were primarily agriculture. Before the American Revolution, the southern colonies mainly relied on growing tobacco as a cash crop, which, in turn, depended on slave labor to be profitable and make fortunes for the plantation owners. After the invention of the cotton gin, the southern states relied most heavily on growing cotton, again a labor intensive form of agriculture that remained profitable because of the low-cost labor provided by slaves. Slaves also were important to sugar plantations in Louisiana and to growing wheat and hemp in many southern states. The United States suffered from a labor shortage at this time and hired help was more expensive and considered more unreliable than slaves, as free people could quit at any time. After the Civil War and the abolition of slavery, the southern economy suffered and the wealthy plantations could no longer flourish.