This book was recommended to me by an avid reader as "the best summary I have seen of the main tenants of Islam and how they relate to the current socio-political challenges of our world." 
 The power of this book is it's focus. Spencer uses primary sources to illustrate, not ALL the tenets of Islam, but simply those that have bearing on the socio-political interaction of Muslims within Islamic society and with those outside of Islamic society (be they co-located or in outside nations). Throughout the book there are recommendations for primary source research should the reader desire more information. 
 Spencer also has an agenda to expose the fallicies of the politically correct presentation of both Islam and Christianity in Western society. While I wasn't too interested in the Crusades section when I picked the book up, Spencer's logic was compelling enough for me to devour these sections when I came to them. His basic point is that both Islam and Christianity are being misrepresented in public discourse. Islam is being presented too favorably, while Christianity is being presented too harshly. The result is a dangerous underestimation of the political threat of Islam combined with an apathy toward Western civilization (and the Christianity it was built upon) which is rendering the West somnolent. This was a compelling arguement that made me recognize my apathy and rethink some of actions. 
 As somewhat of an aside, I should mention that Spencer is intentional about documenting that NOT ALL MUSLIMS agree with ALL the concepts of Islam that he is presenting. But his point is three-fold: 1) We simply don't know a credible way to determine what percentage of Muslims embrace specific doctrines of their faith; 2) The concern remains that if one is truly commited to Islam, this IS what Islam teaches; and 3) While atrocities have certainly been commited by Christians, sometimes even in the name of their faith, an examination of Christianity (via the primary source method Spencer applies to Islam) reveals that Jesus and the Bible neither endorse nor encourage these egregious acts. Which brings me to... 
 Another theme of Spencer's work, though less developed, is that whether or not you agree with Christianity, it's presence was essential to the development of Western Civilization as we know it. The Christian (and in some cases Judeo-Christian) concepts of a natural order, freedom, loving others as yourself, intrinsic law (and therefore the requirement of lawfulness), and compassion for the oppressed, have not only influenced but molded our society into what it is today. Spencer contrasts the Islamic society which was established by Mohammed in rejection of these Judeo-Christian concepts and notes that the two worldviews are drastically different. And not in idea only, for the society created by each is also vastly different, and not many of the West would want to live in the Islamic version. I know I certainly wouldn't. 
 Of course, the challenge Spencer faces is that telling Westerners this different worldview exists and is threatening their lifestyle is kind of like warning fish that water is drying up. Who can really fathom it? In order to increase my own comprehension, I think this is a book I will need to read again. 
 2017 update: 
 This has come to my attention recently, and I've had to look it up a couple of times, so I'm hoping that typing it here will help me remember while also assisting readers evaluating this book. The white supremacist that has come to prominence in the USA recently is RICHARD SPENCER. The author of this book is an entirely different gentleman named ROBERT SPENCER, who is the director of Jihad Watch, a program of the David Horowitz Freedom Center, and the author of seventeen books. His full biography is here: 
 https://www.jihadwatch.org/about-robert