Cities populations grew rapidly as both immigrants and native-born citizens sought higher paying jobs.
Explanation:
This is the main change that the United States experienced between the Civil War and the 1920s. During these years, the United States welcomed many immigrants who were looking for a better life. This was due to the growth of cities and industrialization, which made it easier for people to find jobs in urban areas. People from rural areas of the country similarly moved to cities seeking higher paying jobs.