Final answer:
The Civil War's massive impact on American society, including the shift in economic powers, introduction of federal dominance, and the ethical and human consequences of mass mobilization and slavery, steered American literature from Romanticism to Realism.
Step-by-step explanation:
The aspects of the Civil War that might have caused the dramatic shift from Romanticism to Realism in American literature are deeply rooted in the societal changes and traumatic experiences of the war. As the war revealed and exacerbated political, economic, and social fissures, it also reflected the stark realities of human suffering, sacrifice, and the complexities of moral and democratic issues. This was a stark contrast to the Romantic era's focus on the ideal, the allegorical, and the dramatic. The experiences of mass mobilization, the dramatic political shifts toward federal dominance, the undermining of the South's plantation economy, and the advent of industrial economies in the North, were realities that the American people could not ignore. Furthermore, issues such as the fate of slavery, racial tensions, conscription, and massive causality rates brought a new level of awareness to the everyday lives of ordinary people.
Realist writers like William Dean Howells, Mark Twain, and Henry James sought to portray characters and plots that resonated with the average American, dealing with plausible struggles and not always finding resolution. Their works included three-dimensional characters, ordinary speech patterned after social classes, and plots driven by character exploration of realistic issues. This method of writing was more in line with the lived experiences of Americans post-Civil War and stood in defiance of the previously dominant Romantic styles, which now seemed out of touch with the changed social and cultural landscape.