From The Ashes
From The Ashes by Carl Lynwood Sargent is the second edition of the Greyhawk setting. It was one of the most drastic and skubworthy changes of this era. But first, we need to explain what it was that Sargent broke.
The Greyhawk setting up through the 1980s was an organic process with many, many D&D gamers involved. Most of those gamers had grown up in 1950s-60s America. Whatever their personal differences they shared several traits: an optimistic view of human progress, a deep personal knowledge of European culture and history, an appreciation for post-Carolingian civilisation, and Protestantism in its Anglican / Lutheran form. Together the Greyhawk setting illustrated The Good in its central nations Veluna and Furyondy: quietly religious, militant against clear Eeevil, mostly tolerant. "Evil" included Vikings, Calvinism (The Pale), parodic Catholicism (Medegia), decadent Rome (the Great Kingdom), and of course the chaos in Iuz. For Greyhawk, Islam was something faraway - it wasn't exoticised or "Orientalised", so much as deemed not-a-problem. (Contrast, the Desert Nomad series.) Equatorial rainforests absolutely were exoticised: this is where gamers got the Robert Howard out of their system.
As a result, adventurers in Greyhawk are active - they push forward the borders of civilisation - not reactive. Sometimes adventurers can screw up, and let loose a serious bane like Zuggtmoy in Temple of Elemental Evil or the chained god in that Forgotten Temple of Tharizdun; but this was considered a hazard of the job. Some other adventurer maybe could come by to clean up the mess.
When Lorraine Williams took over TSR, she did away with those old gamers, starting with Gary himself. With Second Edition, her TSR chose to upend the table, with the Greyhawk Wars. The Wars' aftermath is where Carl Sargent came in.
Sargent, as noted in his biography, wasn't all right in the head. He also came with a British viewpoint, which hadn't been the American viewpoint in some generations. For Sargent, the struggle against evil was something visceral and real. It wasn't about taming the wilderness, for him; it was about the Second World War. War itself was a horror; and at the end of the war, the good guys lose ground.
From The Ashes proposes a world in which Iuz has united all the barbarous and also-evil nations in the centre of Greyhawk, and attacked its neighbours; allowing other nations to make separate-peace to expand their own evil. As a result, the Horned Society is simply gone. (This nation returns, in spirit, in Golarion.) The Great Kingdom collapses, to become a chaotic and demonic land like Iuz once was. The Bright Desert is now a new nation - of evil, under Rary, now called the Traitor.
These new evil superpower nations are described as horrific beyond what older Greyhawk had laid out - certainly because Carl Sargent had demons of his own.
Legacy
Greyhawk splatbooks and modules continued to be released for the post-Sargent Greyhawk. These developed the horrors left in its wake. Sargent did many of these himself: City of Skulls, for instance. Eventually TSR itself died and Sargent had to release his Great Kingdom splatbook across the #200s issues of Dragon. And then Sargent himself went poof.
Under the New Management of Wizards of the Coast, the oldest guard and the newcomers agreed on One Thing: they liked the old Greyhawk, not this GRIMDARK para-Warhammer what Sargent had left them. So another Gazetteer came out tamping down some of this stuff.
Perhaps its overall legacy is more pernicious: compare the ill-received 4e incarnation of the Forgotten Realms, and how it similarly tore up bits people liked while introducing new bits no one did in an effort to reinvent the setting entire.