The Baklunish-Suloise Wars and the resulting mutually assured destruction is the backdrop conflict that sets up the World of Greyhawk setting. Not surprisingly, outside the timeline by Gygax there hasn't been much written officially about this war itself which raged from 5031 S.D. to 5094 S.D. (Suel Dating) although the Twin Cataclysms (the Invoked Devastation and the Rain of Colorless Fire) and the Great Migrations preceeding them do get most of the attention when concerning ancient Flanaess history. It is noteworthy that this fictional apocalyptic account was surely born out of our cultural fears during the Cold War. Interestingly, over thirty years later, new allusions could be made about the Baklunish-Suloise Wars in comparison to today's current events. But I won't dwell on that today.
Here is a link to one of my all-time favorite forum discussions on the War. There you'll find loads of information about the War, including speculation that the Baklunish Empire was on the verge of winning.
One rare source about the war published back in 2005, is Creighton Broadhurst and Paul Looby's mysterious ancient battlefield, The Fields of Padyr for the Living Greyhawk Campaign.
For additional flavor, check out the article on ancient Baklunish Armies by Ed Healy in Oerth Journal #22 (illustrated by yours truly).
No one captures the pathos of the
Suel Empire's fall like Erol Otus.