Final answer:
The Fourteenth Amendment, granting citizenship and equal legal protection, had the greatest positive impact on African Americans by establishing foundational civil rights.
Step-by-step explanation:
I feel that the Fourteenth Amendment had the biggest positive impact on African Americans. It not only granted citizenship to African Americans but also provided equal protection under the law, which was a significant step beyond the 1866 Civil Rights Act. This amendment addressed the question of citizenship and equality at its core, ensuring that all persons born or naturalized in the United States were entitled to full rights, including those who had been enslaved. One specific piece of evidence of its importance is how it has been used over the years to require states to protect the rights guaranteed by the Bill of Rights, thus having a deep and lasting impact on civil rights and liberties.