The correct answer to this open question is the following.
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The United States government promoted African-American rights after the Civil War in the form of the creation of important legislation.
We are talking about the Civil War Amendments to the United States Constitution, which aimed to enforce equality in the American society after the Civil War and the end of slavery in the Southern states.
Specifically, we are talking about the 13th, 14th, and 15th Amendments to the US Constitution.
In the case of the 13th Amendment, this legislation prohibited slavery in the United States. The only exception was when it was part of a punishment for the commitment of a crime. The 14th Amendment gave citizenship to all African Americans. The 15th Amendment forbade any government in the US to deny people the right to participate in elections due to the color of their skin or race.