Magic falls from the sky as meteoric dust. Wizards have used it up in places of high population density (except after meteor showers, when there’s a brief Jubilee). But if you’re in a desert or steppe where settlement is impossible, you have magic. This gives nomads an advantage over settled people except near hot-springs, active volcanoes, and other upwellings from the earth’s core.
For millennia, the Ring of Fire has been the bastion of civilization against the depredations of the shamans, but someone has just figured out you can mine magic out of the ground if you dig deep enough.
