In the 1920s, the industry replaced the railroad industry as the country's more vital and important industry

The Automobile

Explanation:

Automobile industry superseded the railroad industry and changed the U.S. economy in the 1920's. Not only did it change American lives in many ways, it also led to increased growth in other industries such as oil, glass and rubber.

in 1897, pershing became a tactical officer at west point, and that's where he was given the nickname "black jack." pershing's first name is "john," for which "jack" is a nickname, and he was a white man who commanded black troops. hence "black jack".