What is the Black Belt of Georgia?

In chapter 7 of The Souls of Black Folk, Dubois describes his journey through Georgia, which included an area in a region known as the Black Belt.
The Black Belt was originally used to describe a part of the United States known for its rich black soil. Because of the fertility of the soil, African and African American slaves were imported to the region in large numbers to work on cotton plantations. For this reason, slaves were profitable there.
The large numbers of African slaves that were imported to the region for plantation labor eventually reached, "...half a million at the time of the war," as is recorded by Dubois.
Eventually, according to Booker T. Washington in his book, Up From Slavery, the black belt became less a description of the fertile soil and more a political term for counties where the population of black people outnumber the population of white people. Areas that historically produced rice, tobacco, and sugar were also considered a part of the Black Belt.
In The Souls of Black Folk, chapter 7, Dubois focuses on a county in Georgia, south of the city of Macon, that is considered the Black Belt. In his description of the landscape and the people during his travels, he emphasizes how the region is highly populated by black people, or Negroes, who at the time were mostly tenant farming lands that were owned by the descendants of former plantation owners. He describes the vestiges of the cotton farming industry that apparently left the people indebted and the land largely neglected due to the reduction of demand and dismantling and replacement of the slave labor system by sharecropping and tenant farming.
Today, the Southern Black Belt refers to 623 counties throughout the south that remain among the most impoverished in the United States. They continue to be rural and agricultural, but due to mechanized technology, farming now requires fewer workers. The population of black or African Americans in the Southern Black Belt remains high, and there has been a return migration of educated black citizens to the region.
So, the term Black Belt, as referred to by Dubois in The Souls of Black Folk has a dual meaning for a region of rich, fertile soil that was largely cultivated to produce cotton and, later, other cash crops in the southern part of the United States. It was in this region that slave labor was in high demand, and a large population of the descendants of those slaves continued to reside in the area after the Civil War. They farmed the land under the subsequent labor systems of sharecropping and tenant farming, which was in practice during Dubois's writing of The Souls of Black Folk.
Perhaps, the term symbolizes debt, impoverishment, oppression, disintegration, shame, exploitation, and ill-gotten gains that led to loss. The allusion to the Bible verse from the book of Song of Solomon at the opening of the chapter provides a clue to the central idea of the chapter, "Of the Black Belt." "I am black, but comely...They made me the keeper of the vineyards; But mine own vineyard have I not kept."
https://southernspaces.org/2004/black-belt/