Congressional Reconstruction began after the election of 1866 gave Republican majorities in Congress. Congress passed Reconstruction Acts that divided the South into military districts and required the former Confederate states to write new constitutions guaranteeing African American rights and suffrage, and ratify the 14th Amendment. This marked the beginning of Congressional Reconstruction, where the terms for rejoining the Union were made more difficult under military control. In Texas, Congressional Reconstruction led to the development of the Republican Party, dominated by Unionists, African Americans, and Mexican Americans.