The effects on the South from the war and the military occupation afterwards were devastating and permanently debilitating. That is what Paisley was singing about. You will not get many honest answers about this because even today, 150 years later, the military occupation of the South is a taboo subject that is completely whitewashed in American history textbooks that confine that themselves to a canon of three standard subjects which are carpet bagging, Jim Crow laws and the KKK. The official propaganda line on all three subjects compares with any Soviet propaganda or worse in terms of sheer lies and misrepresentations. I am not going to go into that further, however, because your question is about long lasting effects of occupation.
I lived briefly in Atlanta in the 1980s, and I can tell you that the downtown might be all glass skyscrapers, but if you went anywhere outside the downtown or Buckhead suburb, to one of the 5 counties surrounding it like Cobb County and Fulton, there is nothing but dust, junked out cars, and people in poverty. Driving through those areas it always seemed like they were still in the middle of Civil War.
After the war the North kept up their economic blockade of the South and this was the main thing which has impoverished them. In the South there were actually "export tariffs", that means you have to pay money to export a good. You may have heard of "tariffs", normally they are taxes on goods coming INTO a country. The North actually put tariffs on goods going out as well as in, basically a blockade. They also used sleazy, backhanded tricks to choke off the South after the war. For example, one trick was mandating so-called "quarantines" on all the southern ports. This meant ANY ship entering the port would be held at gunpoint and forced to stay there for THREE WEEKS before it could leave or transact business. Obviously, you hardly need to use tariffs to block trade when you can just "quarantine" ships.
Because of this, most goods had to be shipped by rail (controlled by northerners of course) to New York for export, which was expensive and economically devastating--essentially condemning the South to poverty for decades because it had no freedom of trade.
Another crushing oppression of the South that has crippled it even today was the destruction of all the printing presses to prevent a record of their oppression from being published. After the North occupied the South, they put all the newspapers out of business and required "licenses" to operate, only allowing a tiny handful of newspapers which were carpet baggers' rags to exist. In some cases they even burned out newspapers or printers, just to make sure they were gone. Because of this, the entire publishing industry of the South was completely annihilated. Ironically, the few newspaper articles about the post-war oppression were all published in the North. Even today, there are very few publishers in the south.
Another consequence of the occupation was the routine burning and destruction of anything in the South that might have value. For example, Alexandria, a large city in Virginia was captured by the North during the war and fortified by them. After the war when the troops were due to leave the city, rather than return the property in the city to its owners, the Northerners looted it and burned it to the ground as they left. This practice was general throughout the South. The Northerners stole whatever was saleable and shipped it to the North and burned or destroyed what they could not transport. This resulted in virtually every factory and business in the South being destroyed. Since technology takes many years to develop, this destruction made the South into a permanently backward part of the country, hopelessly behind in technology.
The human cost was devastating as well. I probably do not need to describe to you what happened to the women of the South during the occupation. The harm of such things are impossible to quantify and long-lasting beyond material loss.