Board Thread:Lore Discussion/@comment-97.81.240.58-20130603234626/@comment-6707115-20130626233758

No, if Ulfric wins the Civil War and gets a peace treaty, he'd be free to attack the Thalmor without Imperial attack (at least until he's done the Thalmor enough damage so that the Empire can snap up both the Dominion and Skyrim). In the Concordat the Thalmor never wrote down a defensive pact, only territorial, administrative, and religious concessions.