The Book above is summarized here, a must read

History of Jihad’s value lies not only in its scope — it covers every single jihad theater, from Arabia to Persia, North Africa to Europe, Spain to India, Tel Aviv to New York City — but also its explanatory power. Spencer relies heavily on primary sources and the words of contemporary witnesses, so the reader gets a good impression of how it was to experience the jihad.

Repeating without fail are cycles of brutality and piety, and the clear religious motives of the Muslims. Jihadists have always been candid about their reason for waging war — to subjugate infidels under the rule of Islam — but people in the 21st century have a hard time accepting this, and have grasped at every possible explanation except the obvious one.

Studies have proven that there is no correlation between Islamic terrorism and poverty; there are as many middle-class and well-to-do jihadists as poor ones. Unlike most of human warfare, holy war is waged primarily for spiritual reward, and it operates irrespective of rational purpose. It takes the guardrails off civilization, and you can’t reason with it. This makes Spencer’s book a horror drama as much as an historical one, and it’s hard to put down.

It’s rare to see myths about Islam debunked so thoroughly, though we got another one recently from Dario Fernandez-Morera in The Myth of the Andalusian Paradise (2016). The reality of Islamic Spain is that there was no fruitful cooperation between faiths. The Muslims were less friendly to Jews and Christians than American Southern whites were to blacks before civil rights. In Spencer’s book, the same conclusion is drawn in all times and places:

“There is no period since the beginning of Islam that was characterized by large-scale peaceful coexistence between Muslims and non-Muslims. There was no time when mainstream and dominant Islamic authorities taught the equality of non-Muslims with Muslims, or the obsolescence of jihad warfare. There was no Era of Good Feeling, no Golden Age of Tolerance, no Paradise of Proto-Multiculturalism. There has always been, with virtually no interruption, jihad.”