[Edi]

If you want to base something on the Cauldron-born and make it a death nation, the name should be Annuwynn, as that was the name of the enemy in the Chronicles of Prydain that Lloyd Alexander wrote. Prydain were the good guys.

I second taking a deeper look at all the five books, because there's a lot more there than in just the Disney adaptation. Or original sources, if you prefer and can get them easily. The entire series is shorter than a single volume of e.g. Robert Jordan, so it's swiftly read too.