What is the concept demonstrated by the growth of factories in the North and plantations in the South?

Just like the Question says, I don't really understand it when it says Concept -___-What is the concept demonstrated by the growth of factories in the North and plantations in the South?
The concept is industrialization in the North and an agrarian or agricultural economy in the South. Concept means the basic idea. The basic idea here is the North relied on industry, the South on farming.