Okay, so why is that? Why do some southern states like Mississippi, belonging to the world's only super-power nation, have such poor life quality, standards of education and so on. If they are on the Mississippi River delta they should, at the very least, have lots of good natural resources to utilise down there. Can you or someone explain this?
Part of the reason is cultural. Mississippi is the poorest state, but it is also the most religious, has the lowest amount of high school graduates, and are also the most obese. People in the south don't view themselves as poor as long as there's a roof over their head, food in their gut, a Bible on their shelf, and a Republican in office.
If you asked a Southerner, they'll probably tell you it's due to history. The Civil War left the South in ruins, and the Industrial Revolution made it worse as it almost completely skipped over the South.
They also don't have major metropolitan areas, with exceptions of Atlanta and New Orleans, and as such jobs are scarce. The Mississippi River Delta is more affluent than other areas as you said (and also more liberal) but only relatively. There is essentially no middle class in the South, everyone is either dirt poor or filfthy rich.
As for how it can be so poor while the USA has become so rich, I guess that's a flaw of the Federalist system. Even when the nation does well, the Southern states will make stupid economic decisions and remain poor.