What if I told you that sometime way down the line time, the laws of physics, & general physics breaks down during Ragnarok. What happens if the gods died, time cracked open, & the Earth almost perishes. You see thousand perhaps millions of years in the future the future cycle of Earth ends possibly due to the return of magick & the Outer Gods. Now AS&SH is a mixed weird fantasy setting based on many of the Lovecraft circle of writers this includes HP Lovecraft himself, Robert Howard, & Clark Ashton Smith. Smith's Hyperborea cycle actually holds the clues. According to the Wiki entry on Clark Ashton Smith's Hyperborea; "Smith's cycle takes cues from his friends, H. P. Lovecraft and Robert E. Howard and their works. Lovecraft wrote to Smith in a letter dated 3 December 1929: "I must not delay in expressing my well-nigh delirious delight at The Tale of Satampra Zeiros [Smith's short story]... [W]hat an atmosphere! I can see & feel & smell the jungle around immemorial Commoriom, which I am sure must lie buried today in glacial ice near Olathoe, in the Land of Lomar!". Soon afterward, Lovecraft included Smith's Tsathoggua (which originally appeared in "The Tale of Satampra Zeiros") in the story "The Mound", ghostwritten for Zelia Reed (Zelia Bishop) in December 1929. Lovecraft also mentioned Tsathoggua in "The Whisperer in Darkness", which he began on February 24, 1930. Because Smith in turn borrowed numerous Lovecraftian elements, the cycle itself may be regarded as a branch of the Cthulhu Mythos. In a letter to August Derleth dated 26 July 1944, Smith wrote: "In common with other weird tales writers, I have ... made a few passing references (often under slightly altered names, such as Iog-Sotot for Yog-Sothoth and Kthulhut for Cthulhu) to some of the Lovecraftian deities. My Hyperborean tales, it seems to me, with their primordial, prehuman and sometimes premundane background and figures, are the closest to the Cthulhu Mythos, but most of them are written in a vein of grotesque humor that differentiates them vastly. However, such a tale as "The Coming of the White Worm" might be regarded as a direct contribution to the Mythos.""
So what's this got to do with Treasures of the Ancients (GWA1)? Well the Hyperborea books have to do with the ending of cycles especially with life, social values, & matters that pertain to the way of life in the capital city of Commoriom. What happens when all of the advanced technology of the Ancients gives way to the reality of magick & the Outer Gods? Much of the old ancient technologies disappear the second that second when the Hyperboreans come to claim the 'Old Earth'.
But where the Hell did the armies of the Hyperboreans come from? They came by the millions from outposts & forgotten cities from the remotest corners of the Earth & from deep within 'Old Earth' itself.
Four Appendix N writers hint about this including A.Merritt's Metal Monster goes into some of the occult technology left behind by the Hyperboreans until their return.
We see more of their legacy with the HP Lovecraft's The Mound. In these novellas & stories the descendants of the originators were seemingly gone & their legacy had been picked up by decadent descendants who brutally & insanely carry out their original missions. We see this getting picked up in A.Merrit's The Moon Pool once more. In all of these stories the invaders from below are brutal, efficient, completely genocidal towards mankind quite literally casting the works of mankind into ruins. We see this theme extended in the footsteps of Bulwer-Lytton, Burroughs, Conan Doyle, and others of the Weird Fiction tradition.
The polar ice caps metal & we are left with mankind's scarps at the remote corners of 'Old Earth'. The first of a series of plagues in the genocidal wake of the summoning of the Green Death happens. Some of the earliest migrations to Hyperborea happen with the descendants of the Esquimaux stock making their appearance in Corey R. Walden's AS&SH adventure The Anthropophagi of Xambaala. We get a glimpse into how the ancestors of tribes came to almost dominate the Hyperborean city of Lomar in HP Lovecraft's story Polaris.
Biological weapons used by the Hyperboreans are left behind in the form of mutants & monsters on 'Old Earth' & Hyperborea in AS&SH. The occasional military artifact crops up from some forgotten bunker or other dungeon ruin.