I have, by the way, updated the website. Including new material.
The Elvis Wars
This book is 'forbidden' mostly in the sense that mundanes don't get to look at it. Soldiers on both sides are effectively cleared for the information, although Hell takes the official opinion that the book is the worst sort of angelic agitprop and outright disinformation, not to be trusted and certainly not to be sought out. This, of course, means that Hellsworn open it right up... which was the Game's intent all along. Talking monkeys are quite predictable that way.
The Elvis Wars is a history of a set of connected campaigns made by Heaven against the Media in the latter half of the 20th Century. Strictly speaking, only the second, fifth and seventh campaigns explicitly involved Elvis Presley, but to most celestials those three sub-conflicts were most representative of the whole. Besides, the causes for the third and sixth campaigns were rooted in events from the second and fifth. In human terms, the Elvis Wars were more about Elvis than the War of Jenkin's Ear was about the ear, but less than the British/Chinese Opium War was about opium.