Ulfric is tearing Skyrim asunder because the Thalmor knew exactly how to manipulate him into doing so. The Thalmor said "Jump" and Ulfric did just that.
It couldn't be that he (and many others) actually wanted Skyrim to be independent of the empire... The fact that the Thalmor think they can manipulate him and the situation is irrelevant from that perspective. And it's irrelevant in fact, if the dovahkiin enters the fight.
And Ulfric DID cause Alduin's return in a way: he made Skyrim "sundered, kingless, bleeding", fulfilling the last part of the Alduin prophecy.
Bleargh. We've been over this in other threads. So did a hundred other contingencies including the birth of a dragonborn. Also totally irrelevant.
The thing about the Stormcloaks' grievance I don't get is this: The Thalmor are the root cause of Skyrim's predicament... so the Stormcloaks blame the Empire? What kind of logic is that? Exactly the kind of logic the Thalmor were hoping for.
For one thing the empire is in bed with the Thalmor so fighting the empire IS fighting the Thalmor- at least their presence in Skyrim. But it is not just the WGC that makes people resent the empire- it's their increasing interference in Skyrim's affairs. The WGC was just the big straw that broke the horker's back. See http://www.uesp.net/wiki/Skyrim:Skyrim%27s_Rule:
But as mighty and influential as each individual Jarl is, Skyrim's true power comes from the strength of its High King. The High King is ruler above all, and is always one of the Jarls, selected by a body called the "Moot" - a specially convened council of all the Jarls, who meet with the express purpose of choosing Skyrim's High King. Or so it is, in theory.
The reality, however, is that the High King swears fealty to the Emperor, and as Solitude is the city most directly influenced by Imperial culture and politics, the Jarl of Solitude has served as High King for generations. The Moot, therefore, is more formality and theater than anything else.
But as I prepared to leave Skyrim, I could feel a change in the air, sense the trepidation of some of the good Nord people. Many seemed unhappy with the Empire's continued presence in their land. And the outlawing of the worship of Talos as the Ninth Divine - a stipulation of the White-Gold Concordat, the peace treaty between the Empire and Aldmeri Dominion - has only strengthened that division.
So while the Jarls of Skyrim still control their holds, and those Jarls are ruled over by their Imperial-sanctioned High King, will there come a day when the Moot convenes to select a new High King - one that is not, as many would say, the Emperor's "Solitude puppet"?
If that day comes, I will be thankful to be far away from Skyrim, in my own home of Hammerfell. For such a decision could well mean civil war, and I fear that such a conflict would tear the fierce and beautiful Nord people asunder.