The Invasion of Zey'knalost was the horrific event that occured 1st Era763, following Zey'knalost's summoning in the Qellmyr ruin of Z'thragok, after Zey'knalost a relatively peaceful Daemic God was driven to madness by his curiosity by reading the Chronicle of Knowledge he conjured portals to his realm, and his Daema crawled out of the sky and began terrorizing Detrus. Imperial forces were well-established in the Empire and defended their cities as long as they could, but the endless river of Daema proved too much, the Empire crumbled after years of invasion, and Zey'knalost merged his realm of Rapture with Detrus and enslaved the remaining mortals.
Thorin Riverwood and K'thasa were able to locate a Chronicle of Time & Space, using this and a Qellmyr Chronicle Decoding Sphere they were able to travel back in time to the point were Zey'knalost was driven to madness and prevent the entire disaster from happening.