From the Introduction Overview:
The Net Book consists of a series of monstrous races and hardy Humans inhabiting and co-operating a beautiful, but harsh
land full of mystery and surprises.
On Mystara, the region labelled 'Hyborea' on the maps of the civilized world shows little of anything and is in essence a "frontier land". This land has its inhabitants, strange creatures who have clung tenaciously to occupation in spite of the most terrible of cataclysms, and the inroads the most
powerful and populous race on Mystara, (the Humans) have made into their cultures.
Some Immortals have protected this area, and have tried to bring these survivors into contact with the more civilized of human political powers in the Known World as equals, rather than monstrous rivals...