Personally, I think people overestimate the power of Wights and Shadows. All it takes to destroy them is a couple Fly spells and a high level Archer or Wizard. It's a nice tactic to gain extra ground troops for a big battle, but I doubt it'd be that effective as your main force. You would need other forces to supplement them, or they would be easily destroyed by flying opponents. And since every race can have Clerics that do this, it's not a real big advantage for any particular race.
Hobgoblins would be very deadly, I admit, but I don't think they would be as tough as Dwarves, as they lack the extra racial bonuses that Dwarves have, and they are also +1 ECL. Still, definitely contenders. I don't really see Orcs conquering the world, as a lack of intelligence combined with a low lifespan and natural tendency to disorder and chaos would prevent them from achieving any kind of long term gains.
Also, in response to Drawmacks post, if we're going to actually follow the rules, Humans would make better advisors and have more knowledge than Elves. With the bonus feat and skillpoints, they probably possess more ranks in Knowledge: (x) type skills than Elves could ever hope to. I'd also disagree that none of the races would want to "challenge the status quo".
You can make great gains in war, in territory, resources, and living space. If the Human popluation becomes too great, who's to say expansion attempts wouldn't be made into the territories of other races? Maybe the Dwarves want to conquer a piece of land they believe holds a valuable resource they want to get their hands on. Perhaps the Elves have discovered an ancient site of powerful arcane magic in the middle of Human possessed lands. Etc., etc.
I'd also like to point out it is unlikely for one race to rule the entirety of the world. This topic is meant to find out what people think would be the most likely race to have the capability to do so. And as such, which race would have the largest and most powerful Empire in a given world.
Personally, judging from the comments in this thread so far, I think the top three contenders are Dwarves, Humans, and Hobgoblins. Goblins might have a chance too, but they are relatively weak and disorganized in most worlds.
