They're a group from Basque France and Spain who were persecuted for hundreds of years starting in the 10th or 11th century and nobody seems to know why. This isn't my direct field, but my understanding is that none of the "usual" reasons apply. They were ethnically and linguistically the same as whichever local communities they appeared in. They weren't heretics and weren't marginalized into one particular and vulnerable-to-scorn job. But they had to wear clothes indicating their status, enter churches through a separate entrance, and there's reams and reams of primary literature wherein folks detail how much they hate the Cagot.

Anyhow, I don't remember if Moore dealt with them, but his book is solid. He writes for an academic audience, but he's more readable than most authors like him if you haven't spent the past decade knee-deep in European religious history.

There was also a really good article at Current Affairs by Daniel Walden that deals with a lot of these themes in order to really pull apart the idea of "The West" as a meaningful cultural edifice. He's a wonderful writer, and also recently wrote a delightfully mean takedown of Ben Shapiro's latest book. Here's the first one I mentioned:

https://www.currentaffairs.org/2018/06/dismantling-the-west