Nightfall said:
			
		
	
	
		
		
			rulesy,
Regardless of that fact let's be factual. Galifar only rule ONE continent and even that was not entirely by his doing. (At least one source I recall mentioned something about the Dragons of Argonssen being involved) So while yes it's possible, I honestly do NOT see anyone ruling the entirity of Eberron, if only because the many OTHER powers that capable of doing epic if not DEIFIC things could concievable start to decimate 10th level PCs.
		
		
	 
Well, Nightfall what I understood from your post was "Yeah [, your PCs could rule Khorvaire] if they were Galifar. Seems to me none of these guys are." My point was merely that actually, any of them 
could be another Galifar with the right ambition and hard work.  I don't think this is a "factual" issue per se, but a question of the direction in which the PCs want to push their characters and the direction in which the DM wants to take his campaign.
As to the other powers involved: Well, sure. That's why I brought up the likely tension in the campaign. In reality, the PCs' actions, if undertaken on a selfish basis and against the legitimate nations of Khorvaire, are likely to help the bad guys (many of whom, as you note, are capable of epic deeds) advance their own position to the detriment of all. But, the PCs 
could end up ruling Khorvaire, if not the world of Eberron, some day. There has to be 
some motive for extending campaigns into epic levels, and IMHO, it shouldn't be about the entire world rising in level along with the PCs or the introduction into the campaign of a "no you can't" mentality and/or high/epic-level NPCs placed there specifically as a foil to the PCs' ambitions. (BTW, I don't see anyone with "deific" power detailed in the sourcebooks, but I'm not an Eberron completist.) 
And yes, you want to avoid the players thinking that wrecking... er, ruling the campaign world should be a matter of hare-brained schemes and instant gratification. That's one reason I suggest confronting any players who try this with the realization that their actions will be potentially putting the world at the mercy of the BBEGs... whom the PCs themselves simply are not powerful enough to take on directly all at once. It's a nice dilemma.