It's funny. It sounds as if his findings were controversial at the time and they still sound controversial or even outlandish. Yet, the way he presents the findings and provides context for them, make the findings seem like common sense. There was a diminishing return on Federal involvement in the South; many people took advantage of the anarchic period that followed the end of the Civil War to enrich themselves and Government expense; the Federal Government is not good at running States and localities; turning a group of uneducated voters on the loose might have some unintended consequences; Southerners might harbor some resentment; problems may arise since the vast majority of the regions wealth has been destroyed; etc (read the intro for the whole list). All of these seem really obvious. Yet, they are not necessarily part of the mainstream presentation on Reconstruction – this book certainly should be. The picture Nordhoff paints is much more nuanced than the official story and when you stop to actually think about it, Nordhoff's story is in many ways more believable.
Review of "The Cotton States in the Spring and Summer of 1875" by Charles Nordhoff
This book presents the history of Reconstruction as it's happening (or just finishing) from the perspective of a keen observer. The whole book is interesting, but most of the major points can be taken from the introduction, in which Nordhoff lists his major findings.