Final answer:
Congress used its powers derived from the Fourteenth and Fifteenth Amendments to the United States Constitution to justify the Civil Rights Act of 1965. These amendments guarantee equal protection under the law and the right to vote, respectively.
Step-by-step explanation:
The Civil Rights Act of 1965, also known as the Voting Rights Act, was justified by the US Congress mainly through its powers derived from the Fourteenth and Fifteenth Amendments to the United States Constitution. These Amendments guarantee equal protection under the law and the right to vote, regardless of race, respectively. This allowed the Congress to enforce the elimination of discriminatory practices, especially related to voting, which predominantly affected African Americans in the United States. The Congress used their constitutional authority to ensure that the promises asserted in the Fourteenth and Fifteenth Amendments were fully realized. The Civil Rights Act of 1965 was one of the most far-reaching pieces of legislation addressing racial discrimination and inequality in the United States.
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