This period is known as the Gilded-Age, which followed Reconstruction and extended between 1865 and 1898, approximately. This was a period of unprecedented economic growth and also of social, political, technological, and cultural changes in the United States. A small but very powerful group of successful entrepreneurs - industrialists and financiers, for the most part - such as Andrew Carnegie and John D. Rockefeller, among others, turned the United States into the largest industrial nation in the world, and also into one of the most modern. These significantly wealthy entrepreneurs established an endless list of cultural and educational institutions, such as museums, colleges and opera houses.
The term Gilded Age was coined by writer Mark Twain.