Vosca is the continent on which most of out attention is focused. It is distinct from Mundus which is the entire physical world.
Multiple times, society in western Vosca has reached what we would call the industrial age, and then collapsed. Each time, this seems to be because the resources the enabled the rise of civilization ran out.
However, because of the persistence of the Genosian Church, there is a sort of un-burnable library that endures through each cycle of civilization and collapse, hence the excruciatingly long calender. Whether or not the entire length of it is true is debatable, and would be difficult for anyone in-setting to really discern given the means available to them.
Generally, Eastern Voscans are analogous to Europeans. It's more complex than that of course, people with access to the interior and southern sea tend to be more Mediterranean in appearance because... Well, that's sort of Vosca's Mediterranean. So Illegonites, Kalmacians, Ibers, a few bits of Galli and the Reich, can get browner than folks in Lendia or the Slivers, Thanemarch and Svitgard. Most of these people are what we would call Caucasian.
Karthack is different. It runs the full spectrum because it's so huge. The Northwestern provinces largely consist of white people with red or yellow hair, barbarians who have been gradually assimilated into the Empire. In the Southeast, a great many of the people, particularly the ruling class, are essentially Izagoni, with deep brown skin and tightly curled hair. In the Northeast, many of the people are of Steppelander stock from their repeated migrations and invasions, in the Southwest, a great many are still of the old swarthy straight-haired Mountain-Stock who once peopled the Viddian Kingdom, the oldest rivals to Karthack and the last of the Twelve Great Cities to fall to Kar-Karthack's dominion. Yet equally East, but South, the Kedouins are lighter skinned than the Eastern Karthacks.