Which side was solely responsible for the end of Reconstruction in the United States?
No side was really solely responsible for ending Reconstruction in the United States, but it was certainly the case that Southern Democrats, known as "Redeemers," had pushed for an end to Congressional Reconstruction for some time when it was finally brought to a close (by getting rid of the few remaining federal troops and military governors in the South) in 1877. This process had really begun in the early 1870s, as some states had already been returned to the control of the Democratic Party. This occurred because powerful politicians were able to forge alliances between poor whites and some business leaders, and it always had the support of secret organizations like "rifle clubs" and the infamous Ku Klux Klan, who aided in suppressing black voters. By 1877, when a political compromise ended Reconstruction in exchange for effective Southern acquiescence in the election of Republican candidate Rutherford B. Hayes, these "redeemers" were already in control of most of the former Confederacy. So Democrats were mostly responsible for bringing Reconstruction to an end. But they did so with the acceptance of many northern Republicans, who lacked the political will to continue Reconstruction in the face of flagging public interest.