Where did the most violent opposition of the reconstruction come from?

The most violent opposition to Reconstruction primarily came from white supremacist groups, most notably the Ku Klux Klan (KKK), which emerged in the South during the late 1860s. These groups sought to undermine the political and social advancements of newly freed African Americans and to restore white dominance through intimidation, violence, and terror. Additionally, local authorities often colluded with these groups, further exacerbating the violence and hindering the federal government's efforts to enforce Reconstruction policies.