...What wold that do to help? Or at all? Would there then be only one emperor, in the entire world? Somehow I'm not sure about that...Maybe you mean one per entity, which already exists as a different tag?
Nope, one per world.
If there are, say, three human civs, they are all loosely ruled by one emperor, that belongs to one of the three entities. Should the Emperor pass away without an heir, the three civs might end up going to war in order to put their own king on the emperors throne (this, in fact, happened a lot throughout history, in Western Europe (the throne of The Holy Roman Empire), in China, and in Japan, and probably other places as well).
Or there could be a handful of emperors, ruling sort of "super-civs", consisting of multiple civilizations that may go to war over land, or resources, or anything, really.
This seems arbitrary. After all, there have been MANY empires at various times, often overlapping, that ruled various parts of the world. Persians, Mongols, Macedonians during the time of Alexander the Great, Aztecs and Incas, Iriquois IIRC, Rpmans, etc. Many of these had overlapping times, and none had particularly notable common roots.
Nothing should be set in stone in my opinion. This idea will become even more interesting when toady puts in procedurally generated races. Also, can someone link me to toady discussing why goblins have no-eat, and under what circumstances it could return? I mean, if nothing else they should raid, and if possible harvest some horrific fungus which grows where they live. Goblins and orcs are exactly the kind of race i can see murdering each other at the dining table in the worse cases.
About NOEAT goblins, I think that, at the time, it was a way to get around goblins' inability to eat veggies, and the worldgen starvation it would have caused.