There were a number of trends occurring in popular literature in the late 1800s. Literacy rates were increasing among the people and so there was a demand for more popular fiction. This generated a boom in "dime novels" that provided excitement for young people. This was also the time of Horatio Alger and his series of books that promoted the idea that anyone could make it in America through hard work and a bit of luck.
On a more highbrow level, this was a time of growing realism in American writing. Mark Twain was active during this time, writing about and criticizing the social and economic systems of the time. Kate Chopin was writing early feminist literature. Stephen Crane became famous for his portrayal of the Civil War in The Red Badge of Courage.
Finally, this was the time of the rise of the "muckrakers." These people wrote books exposing the negative aspects of American life. Many of these books were published just after 1900, but they came out of the ethos of realism and social criticism in literature.