What political party did most African American politicians belong to immediately after the civil war?

No political party. Until the 1965 civil rights act African Americans couldn't vote and even then a voting rights act was needed. Today some states are passing laws to restrict voting, gerrymandering districts, and requiring documents that they know are impossible for some people to have. There is one case of a 90 year old African American woman who couldn't vote because she didn't have a birth certificate. She was born at home 90 years ago. Some states have closed polls, moved them or have shorter hours so people can't vote in the poorest districts. Usually in these districts the population is African Americans. To change these things we need to have everyone vote that can, or drive people to polls who don't have a way to get there.