Immediately following the war all of the Southern states enacted "Black Codes," laws intended specifically to curtail the rights of the newly freed slaves. Many Northern states enacted their own "Black Codes" restricting or barring black immigration. The Civil Rights Act of 1866, however, nullified most of these laws and the federal Freedman's Bureau was able to regulate many of the affairs of Southern blacks, who were granted the right to vote in 1867. Groups such as the Union League and the Radical Republicans sought total equality and complete integration of blacks into American society. The Republican Party itself held significant power in the South during Reconstruction because of the federal government's role.
During Reconstruction, Union Leagues were formed across the South after 1867 as all-black working auxiliaries of the Republican Party. They were secret organizations that mobilized freedmen to register to vote and to vote Republican. They discussed political issues, promoted civic projects, and mobilized workers opposed to certain employers. Most branches were segregated but there were a few that were racially integrated. The leaders of the all-black units were mostly urban blacks from the North, who had never been slaves. Historian Eric Foner reports:
By the end of 1867 it seemed that virtually every black voter in the South had enrolled in the Union League, the Loyal League, or some equivalent local political organization. Meetings were generally held in a black church or school.
— Eric Foner, Black Leaders of the Nineteenth Century
During the 19th century numerous African Americans were elected to the United States Congress, all members of the Republican Party. In the South the party was a voting coalition of Freedmen (freed slaves), Carpetbaggers (recent arrivals from the North), and Scalawags (Southern whites, especially men who had been Unionists in the War). In Texas, blacks comprised 90% of the party members during the 1880s. The first black senator was Hiram Rhodes Revels of Mississippi. The first black representative was John Willis Menard of Louisiana. Over the course of the century, an additional black senator (from Mississippi) would be elected and more than 20 black representatives would be elected from Louisiana, South Carolina, Georgia, Alabama, Florida, North Carolina, and Virginia.
Blacks held other powerful political positions in government. P. B. S. Pinchback was elected lieutenant governor of Louisiana and even served briefly as governor. Pierre Caliste Landry became mayor of Donaldsonville, Louisiana. Edward Duplex became mayor of Wheatland, California.
In the South the Republican party gradually came to be known as "the party of the Negro." In Texas, for example, blacks made 90% of the party during the 1880s. The Democratic party increasingly came to be seen by many in the white community as the party of respectability. The first Ku Klux Klan targeted violence against black Republican leaders and seriously undercut the Union League.
In the 1870s through early 1890s, Democrats in Southern states used various methods to suppress the vote of blacks, largely intimidation, violence and fraud.
Republicans responded by challenging the election results and overturning them in order to count the votes of blacks. This was much more successful when Republicans held an uncontested majority of the US House than otherwise.