The End Times (WAR History and Lore)  

North of the icon for the Great Eagle Nests, inside one of the nests located at 34k/32k is a book titled This Will Be Your Doom. It may be difficult to find as it is partially obscured by the nest, and entering the nest you are greeted with a fairly consistent stream of level 18 Icewing Eagles which will attack you as you try to click the book.

Interacting with the book will grant you the unlock.

History & Lore in Troll Country