Well, why don't we jump forward a bit and throw in the previously-mentioned idea of undead legions?
Say a thousand years has passed, and our scope has greatly expanded again - let's look at a continental area five thousand miles wide. Or rather, an inland sea maybe 5000 miles by 1000 miles surrounded by fertile lands similar to Cresia. Another two thousand miles inland from each coast and civilisation is pretty much lost in wilderness (desert, ice, mountains, I dunno).
Basically the Mediterranean.
If we put Cresia in the middle of the north face of the sea, Ta'jinn extends off to the East. Ausel is somewhere in the north-middle of the sea.
I suggest that the North coast is largely similar to Cresia, with some regions forested, some fertile plains, some hilly, all fading into the northern mountains.
Then the South coast is more fertile, fading into southern desert.
It would be from the South that a new civilisation arises, one with a vaguely Egyptian theme, but modified somewhat by the Auselen Diaspora of a thousand years before. Because what fun is an Egyptian civilisation without (a) blue dragons in positions of power and (b) legions of skeletal warriors? Both things the Auselen Diaspora would have brought to the world, by the by.
Ausel itself is ruled by dragons and formians; it's largely off limits.
Cresia, Stempa and Ta'jinn are still somewhat barbarous. They're culturally assimilated now, although the hobgoblins still keep to the northern hills and the centaurs to the eastern steppes. Somewhat. The whole region is still lacking in infrastructure; rulers include warlords, druidic cults, and clerical cults of over two dozen deities (the Stempan, the Cresian, and the Ta'jinn, as well as various arrangements of pantheons depending on region). There are too many to itemise, at any rate, and the Cresian culture has spread in this form to neighbouring regions despite this apparent lack of infrastructure.
Somewhere to the northwest, a number of tribes of forest-dwellers (guess who?) tell tales of wanderers from distant lands who came bearing eggs a thousand years ago. Some tribes welcomed them, some didn't; those that were trusting found themselves dealing with rapidly maturing dragon whelps within a generation. This region is fragmented too; some groups of elves are independant, while others are dragon-dominated, the dragons and their monks recognising the elven talent for magic and fostering it as a new race of servitors.
Monsters are most common in Cresia, but by now they've spread to every corner of the world. Other magi have committed their own experiments, and the occasional extraplanar explorers have dropped by from time to time. Nothing major, but I think we can assume that just about anything from the core rules is running around ruining someone's life.
And does anyone else thing Egyptian dwarves sound cool?