I have responded to Cavanaugh: here - on the ABC religion and ethics portal. The more I read Cavanaugh's piece, which I briefly discussed here the other day, the less its logic made sense.
You can, I suppose, define "religion" in such a way that "religion" didn't exist before 1700. Up to a point, you can define your terms how you like. But whatever it was that existed before 1700 (something that involved churches, creeds, etc.) certainly was implicated in a lot of violence in the sixteenth and seventeenth centuries, and before ... and that did, indeed, trouble thinkers such as Hobbes and Locke.
In any event, Cavanaugh was foisting on me a simplistic narrative that couldn't be found anywhere in my original piece that he was responding to.