Answer:
...the spread of the railroad
Explanation:
The Postal Act of 1879 increased literacy and reduced cover prices, and the SPREAD OF THE RAILROAD fueled the booming interest in mass circulation magazines after the Civil War.
Postal Act of 1879.
The Post Office Act of March 3, 1879, laid the foundation for modern mail classification by creating the basic mail categories used until the 1990s—first class for letters, second class for periodicals, third class for advertising, and fourth class for parcels.
Monthly and quarterly magazines and trade journals qualified as bona fide periodicals
Publishers were permitted to mail magazines at second-class postage rates. Magazines became America’s first national mass medium by serving as important force in social change, especially I the first decades of the 20th century (between 1900 and 1945.) Number of families who subscribed to one or more magazines grew from 200,000 to more than 32 million.
