Final answer:
Voting rights amendments were not used to disfranchise black voters; rather, they were enacted to protect their right to vote. Strategies such as poll taxes, literacy tests, and grandfather clauses, however, were employed to disenfranchise African Americans.
Step-by-step explanation:
The question refers to methods used to prevent black voters from exercising their franchise in the United States after the end of Reconstruction. Among the tactics listed - poll taxes, literacy tests, voting rights amendments, and grandfather clauses - the only one that was not used to disfranchise black voters was voting rights amendments. These other methods, including poll taxes, which required a fee to vote; literacy tests, which presented often insurmountably difficult assessments; and grandfather clauses, which exempted those whose ancestors had voted before a certain date (effectively excluding blacks), were systematically used to suppress the African American vote.
By contrast, voting rights amendments, such as the Fifteenth Amendment that granted voting rights regardless of race, and the Twenty-Fourth Amendment that prohibited poll taxes in federal elections, as well as the Voting Rights Act of 1965, which banned literacy tests among other protections, were actually designed to secure and protect the voting rights of black Americans.