The Great Plains is the name given to the vast amount of grassland which covers the entirety of central Engelain, reaching from the forests of the elves to the Free Kingdoms, from the mountain-homes of the avians to the edge colonies of the Tyrannian Empire. It is the largest single 'nation' on the continent, though its definition as a nation is incredibly loose. The Great Plains are in the dominion of the one-thousand-and-one herds of the centaurs, and also inhabited by the satyrs. Although the Great Plains has seen its fair share of empires, for the last two thousand years at least it has been unassailable by human-kind.
The earliest recorded settlements upon the Great Plains, (though clearly there were others there beforehand- this superpower simply wiped away all traces of previous civilisation,) was that of the East Great Plains Empire. Five millennia ago, it was the greatest force on the continent, unrivalled in its conquest and unrelenting in its expansionism. A rival force known today as the West Great Plains Empire formed however, and quickly grew to substantial power- perhaps it was a unification between all of the rivals of the original empire. The two waged a grand war against each other, known to historians as the War of Blood and Death, near enough wiping one another from existence.
Their resources depleted, it wasn't long before neighbouring petty kingdoms swarmed into the Great Plains. The centaurs, which had been pushed into the elven forests for centuries, finally came and reclaimed the eastern Great Plains for themselves, whilst in the west a schism between the various avian tribes lead to many hosting settlements in the western Great Plains. The resulting conflicts between man, centaur and avian were cruel, but more importantly they did much and more to wipe out what few traces of these old empires there were- not even their names are remembered today, and to this day no archaeologist has ever found ruins from the West Great Plains Empire, only the east.
Two millennia later signalled the rise of the Casurillion Empire, which was based in Western Engelain and expanded outwards into the western great plains, pushing the grassland avians southwards. However, after the mysterious destruction of their capital, the empire collapsed inwards on itself. The centaurs seized the advantage, and in a series of assaults over many centuries managed to reclaim the entirety of the Great Plains for themselves.
The centaurs lived in relative peace, forming a near-symbiotic relationship with the satyrs, wherein the centaurs would provide them land and protection in return for their wine-yards and other goods. The smaller cousins of the centaurs, the onocentaurs, also existed within the Great Plains, and built great cities out of glass, wherein the light of the sun would reflect through a thousand buildings, and make light which danced through the streets. And of course, at the very south of the Great Plains the grassland avians continued to live, a pleasant and meek people that offered the centaurs little trouble, and so the centaurs did little to trouble them in turn.
It would be many more centuries until the Great Plains was once again faced with attack- the Tyrannian Empire was known to be constantly expanding its border northwards, and the divided centaur herds could do little and less to stop this. The grassland avians were driven to extinction, as were the onocentaurs- their great crystalline towers torn down and sundered forevermore. However, the expansionist period of the Empire was foiled by its own people, with the centaurs taking back their lost land. For four centuries, the centaurs have been the undisputed overlords of the Great Plains, and little seems to be changing that.