The constitutional and social changes that took place between 1860 and 1877 can be seen as revolutionary, though they are not often described using that term.
Revolutionary change comes rapidly, not slowly. It is the opposite of evolutionary, or gradual change, because it is a quick, complete overturn of a prior system. It is, by definition, a startling or shocking change.
Between 1860 and 1877, a foundational, seismic shift in racial relations took place in this country, which had been founded on a social order that, since the 1600s, had accepted the premise that it was right (at least in half the states) for whites to own blacks as slaves.
In 1860, a group of slave-owning states asserted states' rights to try to secede from the union, where they felt under increasing threat that slavery would be abolished. This set into motion a series of events that transformed the relationships between black and white people in this country. In 1863, Lincoln freed the slaves in the South and encouraged them to join the fight to preserve the union. After the defeat of the South, a constitutional amendment freed the slaves and forever abolished slavery as an institution, though it was still allowed in prisons. With the fifteenth amendment in 1870, black men were also granted the right to vote, and in the early years of Reconstruction, efforts were made to economically integrate blacks into the community in a way that would allow them to prosper.
If many of the original aims of Reconstruction were quickly undone, and if Southern blacks in particular continued to face disenfranchisement, terror, and economic oppression, the acceptance of their freedom as a fundamental principle was an enormous change. They went from the legal status of subhuman objects that could be bought, sold, tortured, raped, and even killed by their owners with impunity to having their status as full human beings legally affirmed. No matter how bad their lot was in the South, it was a radical change to be free.