I'm not sure I have much to add to the brief description of this book at Amazon.
It's sort of an update of Clausewitz – updated for the leaders who took Clausewitz's observations to their horrifying, logical conclusions (specifically, Lenin and Mao).
The book is worth the quick read. The topic is certainly deserving of study. It seems our military is always surprised to find that it ends up fighting partisans instead of traditional armies. I'm still not sure anyone has figured out a way to end the partisan war of the 20th and 21st Centuries.
I have one objection which is that the book only went forward from Clausewitz and seemed to "discover" partisan warfare. I'm not sure partisan warfare is so new. I still the Romans developed the only way we know of to end partisan wars: kill enough people and destroy enough property to stop the war. Modern rules of war prohibit this action and consequently modern armies seem unable to win battles against partisans. I just don't think the topic can be complete without also looking backwards.