The political party that most of the African Americans elected to public office during reconstruction was the Republican Party.
After the Civil War, the southern states did not want to grant full citizenship to the African-Americans who had been slaves and Johnson did not want to force them; the Congress of the United States, dominated by the radical republicans, passed over the authority of the President and used the Army to impose provisional governments in the ex-rebel states. It also approved the Thirteenth, Fourteenth and Fifteenth Amendments to the Constitution of the United States to guarantee equality between whites and African-Americans, including the right to vote for them; and forced the southern states to ratify them. Johnson vetoed the measures, but Congress rejected his vetoes and even tried to dismiss him.
Thanks to the reforms, and to the prohibition imposed on the whites of the South so that they could not vote until their past rebelliousness was forgiven and they accepted the legal changes; the republicans gained control of the southern states with the votes of the African Americans, and that, added to their majority in the northern states, guaranteed them the control of power (almost as a single party). This situation lasted a few years.
