Unit 4 discusses regionalism and naturalism in American literature between 1870-1910. Key events included Reconstruction after the Civil War, the Gilded Age of industrialization and wealth inequality, and the rise of labor unions and progressivism seeking to address economic and social issues. Regionalist literature captured life in distinct American regions, using local details and dialects. Naturalist works portrayed humans as helpless against forces like heredity and environment. Authors like Mark Twain, Kate Chopin, and Stephen Crane produced famous regionalist and naturalist works reflecting the realities of the time period.