What we learn from this story about the social and economic changes in the south is reflected in the change of circumstances for Miss Emily that the story portrays. We see that Miss Emily was raised in a mansion, that her father had been a wealthy and powerful man in the town, that his reputation was such that the town's government and its people continued to care for Miss Emily, who is now a remnant of a bygone era, slowly dying, impoverished, in her crumbling manse.
Over all of this hangs the shadow of the Civil War. The story was published in 1930, less than 65 years after the Civil War had ended. We do not know when Miss Emily was born, but we know her father has been buried with the Civil War dead. We can infer that his wealth was founded upon slavery, one way or another, his either having been raised while slavery was extant or having had parents who accumulated their wealth on the backs of slaves. Simply put, the wealth of the south was premised upon slavery. After the Civil War, the south went into a slow slide from which it has yet to recover.
Had the south won the Civil War, become its own nation, and maintained its slave economy, Miss Emily would have had every expectation of being a southern belle, the wealth of the "nation" and her father's wealth having been saved. She would have had no problems financially, and she would have inherited the mantle of her father's wealth and power. Socially, she and others like her would have ruled the town. Her social and economic circumstances in the story, showing her now an impoverished object of pity and curiosity, are a symbol of what has happened to the south.