Final answer:
The Civil War disrupted the social structure of the antebellum South by creating new rights and opportunities for free blacks and freedmen, undermining the plantation economy, and initiating political and social reforms during Reconstruction. The correct option is C. it created new rights and opportunities for free blacks and freedmen.
Step-by-step explanation:
The Civil War significantly disrupted the social structure of the antebellum South primarily because it created new rights and opportunities for free blacks and freedmen (C).
The destruction of the institution of slavery fundamentally altered the Southern economy and social hierarchy. The war undermined the plantation economy, shifted the labor force, and necessitated political and social reforms during Reconstruction. This period saw the advent of new rights for the formerly enslaved, as they sought to integrate into a society that had once considered them property.
Despite attempts by southern states to impose black codes and racial terrorism, the post-war era marked the beginning of a long and turbulent path toward civil rights and societal change. The correct option is C. it created new rights and opportunities for free blacks and freedmen.