What was the significance of Reconstruction for the nation's future?

The Civil War was one of the darkest times in American History. Over 625,000 men would die fighting this war from 1861–1865. Much of the Confederate States lay in ruin. The period after the war is known as Reconstruction. It would become a catalyst for dramatic social changes over the next century.  
The assassination of Abraham Lincoln was a dark day for the defeated south. Lincoln had formulated a plan of amnesty for the former rebels and was determined to let the Confederacy "up easy." Unfortunately, John Wilkes Booth ended any hopes for a quick and painless reconciliation with the northern states. 
Radicals in Congress assumed control of Reconstruction and immediately began to change the social climate in the former Confederacy. The 13th, 14th, and 15th amendments to the Constitution gave former slaves freedom, citizenship and the right to vote. These amendments helped to introduce biracial democracy to the south for the first time. 
Restrictive voting measures such as the requirement to own property, were abolished. In many southern states black voters outnumbered whites. As a result, African-Americans were elected to Congress, including two members of the Senate.
One of the biggest social changes to occur during the Reconstruction period involved education. Schools were funded by state governments and kids of all races were now able to achieve an education. One of the lasting legacies of Reconstruction governments across the south is the land-grant colleges which dot the landscape of the former Confederacy.
These social changes were not without their critics. Some whites attempted to re-establish white supremacy through militaristic groups such as the KKK and the establishment of Jim Crow Laws. The end of Reconstruction in 1877 would usher in almost a century of oppression and discrimination of blacks throughout the south. 
Without question Reconstruction introduced social changes that enabled former slaves to better function as citizens. Those changes would take almost a century to be fully realized as the implementation of segregation in response to those changes made progress slow to a crawl.