The Living Land describes the realm and cosm of Baruk Kaah, High Lord of the primitive reality. This volume explains the situation in North America, including the position of Core Earth USA and connections to other cosm raiders.
After re-reading these rules (a quarter century after my initial read) I still find the initial background of the invasion quite satisfactorily written. I think the reactions to the invasion of earth by a reality with a religion that actually grants miracles lead to some interesting questions the writer tries to address. Is the religion protected constitutionally? Are converts traitors? Some interesting questions to explore through gaming...