The period of Reconstruction took place in the southern United States from the end of the Civil War in 1865 until 1877.
When the Civil War ended, fundamental issues facing the nation included what role former Confederates might play in the US government, and what role freed slaves would play in American society. And the infrastructure of the South, where most of the war had been fought, also had to be rebuilt.
The Fourteenth Amendment to the Constitution was passed in 1868 to guarantee due process and equality before the law for all citizens, including newly-freed slaves. The Fifteenth Amendment, in 1870, stated that the right to vote could not be denied on the basis of race.
New Republican controlled governments were instituted in the South, but were almost certainly doomed to fail. Popular sentiment in the region was obviously opposed to the political party which had been led by Abraham Lincoln.
Reconstruction was, and remains, a highly controversial subject. Southerners felt that northerners were using the power of the federal government to punish the south. Northerners felt the southerners were still persecuting freed slaves through the imposition of racist laws, called "black codes."