With the assassination of Lincoln, the task of binding the country together was left to Ulysses Grant. In the excellent biography "The Man Who Saved The Nation" by H.W. Brands, the extraordinary and often overlooked accomplishments of Grant are finally given their just due.
Not only did Grant militarily defeat the secessionists but during his two terms as president he passed the 14th and 15th amendments, established the Department of Justice to enforce those amendments, fought the Ku Klux Klan, restored federation protection and civil order in South Carolina and Louisiana after they refused to abide by the terms of surrender, and ushered in the first federal civil service to curb the rampant patronage in federal employment.
The author also notes, however, that after the great general’s defeat, his accomplishments were overshadowed by the politics of the late 19th century. Whereas Grant’s approach to reconciliation was premised on the egalitarian ideals of the 14th and 15th amendments, Brands wrote that "Southern Democrats and Northern capitalist-minded Republicans preferred the path of amnesia. The Southern Democrats forgot that secession was about slavery. They recast the Civil War as a difference over states’ rights . . . The Northern Republicans pushed aside Lincoln in favor of J.P. Morgan and company. They transmuted the 14th amendment from a charter of citizenship rights into a guarantor of corporate rights."