Greyhawk: The Iron League

Reggie Dunlop: The Iron League, huh? Lotta' fights? 
Jack Hanson: Nah.

We all know that the Iron League was formed when a handful of small provinces broke off from the southwest corner of the Rauxes-based Overkingdom.  How this was achieved is not obvious until one remembers that the Hanson brothers of "Slapshot" fame were Iron League natives.  Though Jack, Jeff, and Steve had little else to say on their land of origin, one can assume--given their reputation for goonery--that Jack's statement that fighting was not prevalent there must be understood that these sorts of things are, indeed, relative.

Against these dudes, the overking never had a chance.

The brothers, despite their youth and myopia, were big, tough warriors who foiled up their fists before each foray, never backed off from a brawl, and did not hesitate to deliver a low blow to gain the upper hand in a melee.  Sounds like the perfect combination of traits you want in a peoples if your intent is to break away from the largest, most powerful, and most criminally insane regime of the era. 

Oeridi-centric Bias in the Gazetteer

You don't have to read too much of the Greyhawk Gazetteer--or the later Guide edition for that matter--to realize that the thing was written by Oeridians.  And not just any Oeridians; more specifically, the author was most probably a member of the Aerdian clan that pushed eastward into the vast plains of the eastern Flannaes--though he or she is not too happy with the current state of affairs in the once Great Kingdom, he or she clearly takes pride in the past achievements of the Aerdi.  Below are a few of the more obvious indicators as to where the author's loyalties lie.

• Dates are given in CY (Common Year).  This is only done within the current confines of the Great Kingdom.  Most former G.K. states reverted to Oeridian Reckoning--if they ever adopted CY in the first place, beyond "official" ceremony--once they achieved independence from the Overkingdom and non-GK states never adopted the CY reckoning to begin with.  In fact, oddly enough, the Oeridian Reckoning is dominant throughout the eastern Flannaes outside the GK.
• Chronology begins at year 160 O.R.  Ignoring several millennia of history compiled by the Suloise, Olven, Bakluni, and Flan peoples, the chronicler chose a date very near to the Oeridian people's dubious beginnings as the point of origin of the Chronology and Brief History.
• Refers to the Realm of the Aerdi as The "Great" Kingdom.  Outside the current borders of said kingdom, it is rare in the extreme to find someone willing to use that conflated descriptor.  Scholars might refer to it--at best--as the Great Aerdian Kingdom or similar.  In Keoland, the term "Large Kingdom" is used mockingly, stripping the name of its grandeur and also including connotations of excess, as in "portly" or "bloated." The wags of Greyhawk take it a step further, referring to the Aerdian realm as "The Overkingdom" which is a knock on the hubris of the monarch's chosen appellation while also implying that the kingdom has surpassed its date of expiry.
• Assumes that the Suloise migrations into the Flannaes happened over land.  Only the aquaphobic Oeridians would overlook the significance of the sailing culture of the Suloise and assume that they traveled from their southern empire throughout the Flannaes on foot.  In fact, the Suloise had a vast maritime empire for millenia before the Oeridians crawled out of their termite hills in the Steppes or wherever they're from.  Though certainly some large scale movement of peoples occurred through the passes of the the Crystalmist, most major transit of Suel peoples throughout Oerth was by ship.  Certainly the only survivors of the RCF were those lucky enough to escape by sea as only a very small number managed to reach the safety of the mountain passes on foot before being swept up in the conflagration. 
• Implies that the Common Tongue is a product of the Great Kingdom.  While it is true that the Common Tongue is the official language of the G.K., and it is widespread throughout most of the Flannaes, it is not an Aerdian invention, as the Gaz author(s) would have you believe.  Rather, as the Oeridians moved eastward, their spoken tongue was heavily influenced by the Flannish and Suel languages of the folks they met along the way.  What emerged was a Lingua Franca that is an amalgam of the various tongues and cannot be claimed by any single people or nation. The GK claiming ownership of the common tongue is sort of like St. Louis claiming that it is the source of the Mississippi River. 
• Aerdians portrayed as conquering hoard. In fact, they merely occupied the vast, empty plains of the central Flannaes which had been passed over by the Suel and Flannish peoples.  The Flan, being agoraphobes, prefer forests, hills, and mountain valleys to the prairies, and the Suel were, early on at least, leery of settling too far from the sea.  
• Suel portrayed as malevolent slavers. Well, they're not actually wrong; this was true of the old Suloise Empire.  But most of the Suel settlers who came to the Flannaes were refugees fleeing the oppressive regime; a not insubstantial number of them being themselves escaped slaves, and thus, did not carry on the tradition of enslaving others. Often these people were Suel in speech only, having been members of oppressed ethnic groups during their time in the Suloise Empire.