I think perhaps that the influence the bloody American civil war had on subsequent literature would probably be relative to the hard realities of the battlefield and life in the army camps as experienced by the ordinary e a soldiers on both sides of the conflict as opposed to the lofty ideal of opposing slavery could be a reason why realism returned to American literature.
The Civil War was a traumatic and destructive conflict that remains the bloodiest war in US history. Realism began around the end of the war in 1865. Rejecting romantic-era ideals that focused on allegorical characters, symbolic settings, and dramatic subjects, realism depicted ordinary people in everyday situations. What aspects of the Civil War might have caused this dramatic shift in style, form, and thematic discourse in American literature?