But then for the rest of the talk, Armstrong said, audience members "are insisting that [religion] is the chief cause that is to blame." In her book, she writes that she has "heard this sentence recited like a mantra by American commentators and psychiatrists, London taxi drivers and Oxford academics." Religion may not have caused all the wars in history, these people say, but it is inherently violent in a way that has undeniably shaped world history for the worse. It's this ambient suspicion that Armstrong seems to be arguing against, rallying textual evidence from thousands of years before Christ through modernity.

Although the book is framed as a polemic response to what is essentially a straw-man question, Armstrong has isolated an interesting quality of contemporary discourse about religion: It's really, really vague. Contemplating whether violence is inherent in religion might seem like a pastime limited to college debating societies or educated retirees who have a lot of time for book talks (or dilettante journalists, for that matter), but this idea has an intangible and problematic power in Western culture—the focus of Armstrong's study. Even posing the question at the center of Armstrong's book assumes that there's a unified thing called "religion" that has stayed constant over thousands of years of human life.

But, as Armstrong points out in the book, "there is no universal way to define 'religion,'" particularly when it comes to comparing mono- and polytheistic faiths. "In the West we see 'religion' as a coherent system of obligatory beliefs, institutions, and rituals ... whose practice is essentially private and hermetically sealed off from all 'secular' activities," she writes. "But words in other languages that we translate as 'religion' almost invariably refer to something larger, vaguer, and more encompassing." This is an important premise of one of Armstrong's main arguments: It's impossible make a coherent case about the role of religion in warfare and violence throughout history and across the world, simply because religion plays very different roles in different cultures.

For example, religious belief and practice in, say, ancient Mesopotamia were very different than what they have become in modernity—a period that Armstrong and many academics say began in the West in 1648, when peace treaties ending several major wars in Europe were signed in Westphalia, a region in present-day Germany. She describes the spread of more secular governments in the West and the decline of religion as a primary organizing force in many people's lives during this period. Although "religious" violence has always had a political element, she argues, the political nature of warfare—even in wars with putatively religious justifications—has become even more pronounced in contemporary history.