Ulfric was, for lack of a better term, a useful idiot for the Thalmor. So buried in his own beliefs that he couldn't realize that the Empire was in the process of rebuilding for another round against the Aldmari while High King Torygg respected him enough to be convinced to break ties with the Empire over Talos worship if asked. By starting a civil war in Skyrim, it killed the proverbial two birds with one stone: It kept the Empire wrapped up in trying to keep Skyrim while also giving them an excuse to clamp down on Talos worship. Their only real worry was that the civil war would end, as the victor would be able to reunite Skyrim and either resume Talos worship or strengthen the Empire.

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CdrMike, Overwatch Reject