Rabelais said:
Orcs, Gnolls, Hobgoblins, Kobolds, Halflings
There are so many different races, and some of them are nomadic/Semi-nomadic, and most of them are entirely hostile. Governments are incapable of exercising power outside of their spheres of influence. Even presuming that there's a powerful central government. Wouldn't we be looking at City-States rather than a unified national government?
Chimera said:
And all things considered, I have to go back to some of my own PBM experience from the pre-internet days. The leader of a faction wasn't necessarily the smartest, or most powerful, or the senior most. In many cases, it came down to 'who is least opposed to the idea of doing all this work?'
To me, both of these are very, very true. Pratchett takes the same approach in his Ankh-Morpork Discworld books. The Patrician is hardly the most dangerous physically. However, he's the one who does all the work.
And yes, I think that city-states is a MUCH better model than nation states. Never mind that nation states are horribly anachronistic in D&D, it just makes much more sense given the high level of individual power that very large political bodies would be extremely difficult to manage. The existence of HLC's and HL monsters simply make travel too difficult to properly have a large nation state.
City states would be much more feasible IMO. Each city state is ruled by a HLC (or possibly HL monster) and controls the surrounding area of peasantry. Something to remember is that nation states require huge amounts of infrastructure and population to work. IMO, any nation state that attempted to amass that much land would get smacked down by neighbouring city states in fairly short order.
There is also the point of speciesism as well. Why would elves, for example, who remember when your human ancestors were scratching themselves in a tree, possibly join a nation of humans?

Trying to build any sort of nation is extremely difficult in the RL where it is marginally possible to have homogeneous populations. In a D&D world, it would be virtually impossible to get any large body to agree on what a nation should be.
I really do like how Scarred Lands did this - mostly nation states with one or two nation states ruled either by gods (such as the Chardunni Dwarves) or extremely powerful individuals backed by gods (such as Calastia).