For example, you could ask:
* "What were the dominant themes of American literature during the American Renaissance (1830-1870)?"
* "What were the dominant themes of American literature during the Harlem Renaissance (1920s-1930s)?"
* "What were the dominant themes of American literature during the Beat Generation (1950s)?"
Once you specify the time period, I can give you a detailed answer about the dominant themes of American literature during that era.