...So how do historians argue for this kind of homogenizing process? Heather here gives us a key component of this loss of perception. Take a strict cultural relativism — all cultures are equal; import it into ancient and medieval history — there is no real difference between late Roman culture and that of its barbarian successor kingdoms; stir a bit, and you come up with a mild and unalarming reading of what may be the single greatest cultural regression in recorded history.

After baking this recipe for a generation (in which post-colonial paradigms dominated much scholarly attention), what do we have? Several pearls of wisdom: Nothing dramatic happening, no threatening collapse, just a smooth transition. So either we have nothing to learn from the “fall of Rome” about our current conditions or, still better, we have nothing to fear from the challenge of Islamism to Europe. If this sounds like the kind of thinking that dominated French public discourse at the time of the Ramadan 200[5] intifada, it’s because it is...