Erset

I would like to state for the record that
a) It is hard to find any Sumerian online.
b) The words Google does give me look really odd written in English script - which they are slightly wrong.

They call them the rakbene. One human in ten thousand, who is born with the favor of the gods upon them.
When grown, they stand eight feet tall, with silver skin, and eyeless faces. Around their heads, are horns in the shape of a crown, and from their back sprout great golden wings (both horns and wings grow at puberty). They are, in short, hard to miss.
And they are kings and queens, in almost every case. No human can stand against them, and in almost every case, they are cursed with overwhelming ambition. If they cannot rule, they die in the attempt.
And once they have become rulers, their ambition drives them towards conquest. Their gaze falls upon the land beyond their borders, and they war with each other.
As they grow older, they also tend to grow calmer, and subtler. They forge alliances, make treaties, and even groom heirs. Everything, however, remains ultimately in service of their ambition - few of them will not break any agreement they have made, if that is the course that will most benefit them.
This is not to say, of course, that there are no exceptions. Beings with free will have an annoying tendency to deviate from the norm. But the weight of expectation is a powerful influence, and those who still choose to act differently tend not to be of particular historical significance. Or, indeed, to be live very long - their more ambitious kin regard them as potential threats to their power.
This, indeed, is the fate of most of the rakbene born. For most of the word is now ruled by rakbene, and most are not fond of threats. Thus, those who they are not grooming as their successors or vassals, they often have executed.
But some, whether because they are useful tools whilst they can be controlled, because they are not quite willing to kill helpless children, or for any other reason, do not hold such a policy. And so, rakbene do exist who are not (or are not yet) rulers in their own right. Such kingdoms, naturally, often become havens for those who have given birth to a rakbu child.
As has been noted, the rakbene rule most of the known world - they are stronger and faster than a human, steel breaks against their skin, and many have supernatural powers. It is rarely possible for anyone who is not a rakbu to stop them from doing anything much. And those nations who are not ruled by one, tend to be conquered rather quickly by a neighbour who is.
But they do not quite rule the entire world. There, are, of course, the Unknown Lands, which lie beyond the horizon. They have not yet been conquered, or even mapped, for the simple reason that shipbuilding has not advanced to the point where it is possible for ships to reliably reach them. The occasional ambitious rakbu sends a fleet out with ambitions of spreading their reach to an entirely new land. But, invariably, the cost will either quickly dissuade them, or make them easy prey for their hungry neighbours.
And then, there are the Masku republics, the human nations which have retained their independence by the simple method of hiding the entire country.
As one might imagine, the process of hiding an entire country is more easily said than done. Traditionally, the Masku republics are located in the mountains in the most literal sense - they are dug into excavated holes in the rock, connected to the outside only by cleverly concealed doors in the rock. But some are in other places - Masku republics can be found both in the desert and the deep forests. These tend to be nomadic in structure, to make up for the simple fact that they are not as well concealed as are their mountain-dwelling brethren.
Despite this diversity, there are significant similarities between most of the Masku republics.
Firstly, that they are indeed republics - almost universally. Those who hate the rakbu enough to be willing to live in mountains and forests to avoid their rule, tend also to dislike the system of government they represent. And so, Masku culture is strongly opposed to monarchy, and any Masku nation which does adopt a monarchy tends quickly to become diplomatically isolated from its brethren.
Secondly, they are heavily reliant on trade. Although they tend to be just about able to feed themselves (noone outside the Masku is entirely sure how they manage this), the environments they tend to live in makes trade vital for anything beyond survival. Thus, Masku merchants can often be found throughout the world. Needless to say, many of the rakbu would absolutely love to capture such a merchant, so they could find the republic they hail from - which is why such merchants universally carry poison, and will kill themselves upon arrest. And, as a result, rakbu monarchs rarely bother to arrest them, and they are allowed to move freely. In any case, most of them consider it better than allowing their own citizens to leave the country.
Thirdly, they are very small. Despite all their precautions, Masku republics are occasionally discovered by outsiders - and so, they tend to divide themselves as much as possible, in order to survive such things.
And finally, they kill babies. Rakbu are still born in the Masku republics, and they would not have remained republics if they had been willing to let such people grow up. And so, they are euthanised when they are still babies. Needless to say, mothers often object to this practice, and so most republics are very careful to ensure that newborns are not hidden from them (which is made much easier by their small size. Nevertheless, rakbu born locally are the leading cause of Masku republics being conquered.
There is little else to say about the world of Erset. Economic and technological progress is slow - as is population growth - thanks to the warlike tendencies of the rakbu, and their aforementioned unwillingness to allow their subjects to travel. Countries rarely last more than two or three generations, and there are very few great thinkers who have had a chance to do anything of note - fewer still who have been remembered.