Sometimes in history the amplification of the obvious provides insight that is hard to ignore. This is the case with William Dunning’s observation about the ratification of the 13th Amendment and Secretary Seward’s announcement on December 18, 1865.
Thereupon the constitutional provision which excluded two-fifths of the slaves from the population by which the number of representatives in Congress for any state was determined became of no effect, and each of the former slave states was entitled to an increase of members. That the result of the war should be an accession of influence in Congress to the South, was a proposition which few northerners could contemplate with entire equanimity.
In a murder case this would be known as motive. It is evidence of the complexity of a situation which is often characterized as problematic largely due to the racial attitudes and racism of Southerners. The heavy handedness of Congress was needed for the South not to revert to white supremacy. Dunning is pointing out that it is not that simple.
Without some disenfranchisement (some say it has been exaggerated) of white Southerners and massive registration of blacks to vote, Republicans would not long maintain control of Congress. This at a time when black suffrage in the North was far from universal. There is significant evidence of resistance to black suffrage in Northern and Western states. Ironically, it would have made little to no difference in election outcomes due to the miniscule black population in those states.
What is missing in much of the modern discussion of Reconstruction is understanding and intellectual honesty regarding the position of the South at the end of the war. The predictable human reaction to the harsh policies emanating from Washington D.C. was ignored. Back any people against a wall and you experience the best and the worst of them. Power politics does not care though.