It has been fashionable for many years to decry the From the Ashes boxed set as the beginning of the ruination of the World of Greyhawk Fantasy Setting, as it turned many well-established Greyhawk institutions upside-down, wreaked havoc with political boundaries and alliances, and generally shook things up beyond recognition in some cases.
I don't happen to share the loathing of FtA that many of my fellow Greyhawk fans feel towards this product. True, Gygax didn't write it, and I'm not a particular fan of "advancing the timeline" in any sense, but if it has to be advanced, FtA does a decent enough job of it. It certainly doesn't present any changes more drastic than our own history has evinced.
In the course of a few years of Flanaess history, we see the Great Kingdom fracture into ruin; Iuz expand to conquer the Bandit Kingdoms and Shield Lands; the Rovers conquer Tenh; the shadowy Scarlet Brotherhood take over the Hold of the Sea Princes; Geoff conquered by giants, and more changes.
But stop a moment to reflect on some of the changes in European history during the Middle Ages. William the Conqueror, based in a small duchy which would measure only four or five hexes across on the Greyhawk map, managed to take over one of the more prominent kingdoms of the day. The events that led to the event, from the ascention of Harold to the throne of England to the battle of Hastings took less than a year to unfold. A very small power defeats and conquers a much larger one.
In 500 CE, the Visigoths ruled a kingdom that spanned from Paris to Gibraltar. Within a few years of the death of the strong Visigothic king Alaric, the kingdom was fractured and many parts lost. Internal strife and weakness leads to division and defeat, much like we see in the Great Kingdom.
In the early 13th century, an order of fanatical warrior-monks spearheads a crusade and succeeds in conquering large swaths of territory, bringing them under its sway to advance their own religiously-based ideology. The Teutonic Knights are not so far removed from the Scarlet Brotherhood.
Obviously, these are not perfect analogies, but I trust the point is made. Those who complain that From the Ashes changed the map, upset the political order, laid low the mighty and brought the minor to prominence, miss the point of the ebb and flow of history. The modern nationalities that we commonly recognize (France, Spain, England, Germany, Italy) are relatively modern notions, and were in years past quite mutable. Just ask the leaders of once-mighty states such as Burgundy, Catalonia, Lombardy, and the Norman Kingdom of Sicily. That sort of fluidity is part and parcel of the historical landscape, and no campaign should ossify its borders and cultural background without an excellent reason. Even (especially) Rome was fluid, never enjoying exactly the same borders for more than a few years during its entire history. Why should a campaign world be more static?