Slavery expanded after the american revolution for all the following reasons, except:
a. the cost of slaves decreased
b. the cotton gin made cotton production more efficient
c. western expansion and the defeat of native tribes opened new land to plantations
d. northern and overseas textile mills increased and expanded production

regarding the law, the 15th amendment was specifically designed thinking in the rights of black free men.

even though ratified on february 3, 1870, the promise of the 15th amendment would not be fully applied for a long time.poll taxes and literacy tests would allow southern states disenfranchise african americans. only in 1965 the voting rights for african americans would be actually able to vote in the south.

in 1965, president johnson signed the voting rights act, which aimed to overcome legal barriers that prevented african americans from voting as it was guaranteed by the 15th amendment to the u.s. constitution.

i think that the right answer is the aztecs

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