Final answer:
Many white Southerners refused to accept equal rights for Blacks, which posed a major challenge for Republican governments trying to protect the rights of freedmen in the South.
Step-by-step explanation:
A major challenge for Republican governments in the South trying to protect the rights of freedmen was that many white Southerners refused to accept equal rights for Blacks. This resistance to granting black people the same rights as white people hindered the efforts of Republican governments to enforce laws that protected the civil and political rights of African Americans. White supremacists and paramilitary groups, such as the Ku Klux Klan, used violence and intimidation to prevent African Americans from exercising their rights and participating in the political process.