http://www.pbs.org/wnet/jimcrow/stories_events_reconstruct.html
Reconstruction, 1865-1877
Reconstruction generally refers to the period in United States history immediately following the Civil War in which the federal government set the conditions that would allow the rebellious Southern states back into the Union. (The precise starting point is debatable, with some prominent scholars arguing that Reconstruction actually began during the war.) In 1862, Abraham Lincoln had appointed provisional military governors to re-establish governments in Southern states recaptured by the Union Army. The main condition for re-admittance was that at least 10 percent of the voting population in 1860 take an oath of allegiance to the Union. Aware that the Presidential plan omitted any provision for social or economic reconstruction -- or black civil rights -- the anti-slavery Congressmen in the Republican Party, known as the Radicals, criticized Lincoln's leniency.
The Radicals wanted to insure that newly freed blacks were protected and given their rights as Americans. After Lincoln's assassination in April of 1865, President Andrew Johnson alienated Congress with his Reconstruction policy. He supported white supremacy in the South and favored pro-Union Southern political leaders who had aided the Confederacy once war had been declared. 

Southerners, with Johnson's support, attempted to restore slavery in substance if not in name. In 1866, Congress and President Johnson battled for control of Reconstruction. The Congress won. Northern voters gave a smashing victory -- more than two-thirds of the seats in Congress -- to the Radical Republicans in the 1866 congressional election, enabling Congress to control Reconstruction and override any vetoes that Johnson might impose. Congress passed the Reconstruction Acts of 1867 that divided the Confederate states (except for Tennessee, which had been re-admitted to the Union) into five military districts. Each state was required to accept the Thirteenth and Fourteenth Amendments to the Constitution, which granted freedom and political rights of blacks. 

Each Southern state had to incorporate these requirements into their constitutions, and blacks were empowered with the vote. Yet Congress failed to secure land for blacks, thus allowing whites to economically control blacks. The Freedmen's Bureau was authorized to administer the new laws and help blacks attain their economic, civil, educational, and political rights. The newly created state governments were generally Republican in character and were governed by political coalitions of blacks, Northerners who had migrated to the South (called "carpetbaggers" by Southern Democrats), and Southerners who allied with the blacks and carpetbaggers (referred to as "scalawags" by their opponents). This uneasy coalition of black and white Republicans passed significant civil rights legislation in many states. Courts were reorganized, judicial procedures improved, and public school systems established. Segregation existed but it was flexible. But as blacks slowly progressed, white Southerners resented their achievements and their empowerment, even though they were in a political minority in every state but South Carolina. 

Most whites rallied around the Democratic Party as the party of white supremacy. Between 1868 and 1871, terrorist organizations, especially the Ku Klux Klan, murdered blacks and whites who tried to exercise their right to vote or receive an education. The Klan, working with Democrats in several states, used fraud and violence to help whites regain control of their state governments. By the early 1870s, most Southern states had been "redeemed" -- as many white Southerners called it -- from Republican rule. By the time the last federal troops had been withdrawn in 1877, Reconstruction was all but over and the Democratic Party controlled the destiny of the South. 

-- Richard Wormser