A while back I was outlining a fantasy that took place in a world where the great nations of the world were ruled by a Mageocracy.
Magic in that world, was a genetic trait that was more or less random, but had a favoring of specific bloodlines(e.g. two wizards are more likely to have magical offspring perhaps as high as 50/50 chance, at the cost of low fertility), to the point where perhaps 1 or 2 in a hundred people born had the magical gift, and of those perhaps 1 out of 10 were truly powerful.
Thus the societies were built around a magical feudal systems, where the most powerful mages(being proportionality infertile), were the rulers and had massive harems in order to try to continue their blood line. As the magical ability of person decreased, they took their respective positions on the feudal totem pole, with the majority of the "non-magical" making up the serf class. When a child born amongst a serf family had the magical gift(which by law was detected by forcing all children to be tested at a few months of age), the child was removed from the household and trained in the magical arts. Depending on his/her abilities, that more or less determined their social standing. However a person could always try to advance through a fight to the death, and in some empires it wasn't uncommon to have rulers overthrown every few years.
In this world I made up, there was one small nation that was isolated from the rest of the world(On a mountainous island in the northern part of the western ocean), that was magically stunted and the population was devoid of magical ability. For thousands of years, they plied the oceans, and only made contact with the mainland for purposes of trade. This made the non-mages more less small potatoes to the various mage nations, and no significant interest was taken, given that the super continent of the world was more or less staked out, and few of the mage nations had navies(almost all of the battles were land based).
Eventually the non-magic nation started to advance in technology, and they started to trade ever more complex trinkets, and other devices(the mage based societies technology more or less was frozen at about 14th century tech, albeit having through magical means a lifestyle that was about 19th century level for a noble), and eventually drew the attention of the various magical based empires. This eventually leads to the discovery of the location of this island(which is pretty large), and the mages manage to ascertain the development of the non magical nation. Seeing the state of it(it was of about early 19th century technology, they'd just discovered the steam engine and had been using flintlocks), the mages meet and form a large alliance between the warring nations to wipe out this threat.
The story I was working on took place about 1000 years later(it took about the first 40 years of that for the mages to finally conquer the island, at the cost of many hundreds of thousands of lives), when the technologically advanced people are all but wiped out. However, the technology based people, seeing the desparate situation that was happening during the invasion, managed to kidnap and brainwash(through horrendous torture) a powerful mage to enchant a 6 shooter with all of the knowledge of their people, however it was enchanted in such a way as to kill any magic using person(it caused the person to turn the gun on themselves and blow their brains out). After its completion, a small team of men was selected to flee to the mainland, as a means of being the "insurance" in case the islanders couldn't repel the invasion. Unfortunately due to a large storm the small sailing ship of this islander team floundered on the rocks at the shore of the supercontinent, thus ending forever the existence of the islanders.
However, the gun(it was sealed in a special "suitcase" that was largely impervious to the outside elements, given that it was made of bronze and had a vacuum drawn in the case to force it closed) was later rediscovered, at a point in time when the islanders had become little more than a legend(the mages murdered all of the non-magical soldiery that were involved in the war, and purged most of the knowledge of the event from recorded history). The story begins here when a thirty year old fisherman, discoveres the "suitcase" after he dredges it up in his gill net.
I always liked the idea, but I'm just kind of hung up on how to fill out the story. It's just an idea of mine that's been bouncing around.