Can someone tell me all the reasons Ulfric started this Civil War?
I'm of the belief at this point, that it was the design of the Aldmeri Dominion. They want anything that will weaken the Empire to happen, and this is definitely one of those things. I wouldn't be surprised if they planned on attacking following the conclusion of the Civil War, when Skyrim is at it's weakest.
That is a simple, yet incredibly complicated answer and the issue of much debate. There really isn't any definitive answer to be had, and you will get a damning or flattering reason based on who you ask. Imperials will tell you that he is simply a short sighted self-serving manipulator who only seeks to claim the throne of High King, while Stormcloaks will tell you he is a freedom fighter who seeks to liberate Skyrim from an Empire they see as weak puppets of the Thalmor who no longer deserve Skyrim's loyalty.
Very true. To be honest the truth probably lies in between these two extremes. There is no doubt in the actual course of events, all sides seem to agree on that regard. The problem lies in people's views on the causes.
I honestly believe that the Empire never truly intended to enforce the WGC's terms with regard to Talos. As long as people kept it on the downlow I think the Empire was willing to ignore it. At the same time I think the Empire made a dumb move in using Ulfric like that so soon after the end of the war.They had to have realized what would come from it. They knew the Thalmor would be watching. Ulfric is legitimately upset at the Empire for what they did. In the end both sides are at fault but all they do is blame the other.
That being said I don't believe that the Thalmor started or urged the starting of the Stormcloaks. I believe that the rebellion was a natural outgrowth of Ulfric and the Nord's anger. Once the seeds of the revolt were sown I doubt that the Thalmor were slow in taking advantage of this. They may not have started the rebellion but the Thalmor have certainly inflamed it.