The best answer would be that "<span>The GNP rose dramatically and the United States changed from a debtor nation to a creditor nation" but the middle class definitely improved as well.</span>
The history of the United States from 1865 until 1918 covers the Reconstruction Era, the Gilded Age, and the Progressive Era, and includes the rise of industrialization and the resulting surge of immigration in the United States. This article focuses on political, economic and diplomatic history.
This period of rapid economic growth and soaring prosperity in the North and the West (but not in the South) saw the U.S. become the world's dominant economic, industrial and agricultural power. The average annual income (after inflation) of nonfarm workers grew by 75% from 1865 to 1900, and then grew another 33% by 1918.
In his 2008 article for the New York Times, James Gleick talks about "the gloom that has fallen over the book-publishing industry" to describe the the negative impact of digitalizing books in the book-publishing industry.
In this article he describes the already decline in paper-books sales due to the rise of digital platforms such as Kindle, epub, etc, and how the future of book-publishers looked grimer because of an agreement between authors, publishers and Google to allow the scanning and digitalizing of books to make them accesible in website and digital platforms.
This agreement would be dramatic for the sectors of the book-publishing industry dealing with marketing, archiving and distributing physical paper books.