Sounds like an interesting idea, and a good way to add flavour to your games - bands of Templar like warriors fighting for 'good' clashing with necromancers' bands, etc.
However frostgrave does already have a brief history description, though there's definitely room to expand on it and make each gaming group or individual's frostgrave unique.
Frostgrave is set in the old city of Felstad, a once great city, centre of a mighty empire, and home to many wizards and their magical treasuries, and their undead servants and construct guards. However somehow a magical accident occurred which caused a great storm to appear over thecity, burying it and it's inhabitants under a great frozen snowdrift.
More than a century later the frost has started to thaw, drawing in wizards, their students and mercenary bands in search of the lost magical treasures and knowledge.
The living inhabitants of frostgrave did not survive the freeze. The only inhabitants now to be encountered are those who were not alive so therefore could not die but were merely frozen in their undead (or man made animated)state and thawed out with the ruins of the once great city, and the wild creatures who have made the ruins their home.
Now it would appear that a powerful lich lord had made a home in felstad long before the freeze and like the other undead was frozen and has since thawed out. Now he is drawing darkminded men and women, including wizards, to his side as well as commanding legions of undead.
Under felstad in a labarinth of underground chambers are many hybrids of creatures descended from the experiments of the beastcrafters in the breeding pits.
Like I said there's room for making it your own
Thanks for sharing your ideas