What period was Carnegie describing in the excerpt wealth?

In the excerpt from "Wealth," Andrew Carnegie describes the late 19th century, a time marked by rapid industrialization and economic expansion in the United States. This period saw significant wealth accumulation among industrialists and entrepreneurs, leading to stark contrasts between the affluent and the impoverished. Carnegie emphasizes the responsibilities of the wealthy to use their fortunes for the greater good of society, reflecting the social dynamics and moral considerations of his era.