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The way I see it, Titus Mede didn't realize that no matter what, the Thalmor mustn't be given the opportunity to get footing on the mainland, not to mention land populated largely by humans. I have no doubt that Skyrim united with Hammerfell could fight this two front war and win. The fact that they tried to kill Ulfric is proof that the Empire needs to be destroyed as well. With a little planning the Empire could help Ulfric defeat the Aldmeri for good. Ulfric's best move would be to unite with Hammerfell and march into Summerset Isles and lay waste to the Aldmeri. Think about it, if Skyrim became independent then whatever they do is not the responsibility of the Empire.
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The fact that they oppose this, is proof that the Empire has become corrupted or infiltrated by the Aldmeri. It is in the Empire's best interest for Ulfric to become High King of Skyrim and withdraw from the Empire. Hammerfell fought the Aldmeri to a standstill, granted the forces of the Aldmeri were weakened from the war with the Empire, but they fought so well that the Aldmeri had to withdraw from Hammerfell. The Empire didn't help Hammerfell because it would have violated the treaty. Southern Hammerfell was, after five years of continuous warfare, left in a devastated state, and Hammerfell remained an independent province. The Redguards were eventually able to fight the Aldmeri to a standstill, leading to the Second Treaty of Stros M'kai in 4E 180, which dictated a complete withdrawal of Aldmeri forces from Hammerfell. Hammerfell, however, was unwilling to accept the loss of so much territory and continued to fight, forcing Titus II to officially release Hammerfell from status as an Imperial province in order to maintain the treaty. The Concordat's terms also included the cession by the Empire of a large portion of southern Hammerfell to the Aldmeri Dominion.
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After learning this, I understand Ulfric's motives better and I find myself agreeing with him now. I can easily see Ulfric leading Skyrim to an alliance with Hammerfell and the Nords and Redguards defeating the Aldmeri and then dismantling the Empire. Hammerfell fought the Aldmeri to a standstill. The Empire abandoned Hammerfell because of their refusal to give up so much territory to the Aldmeri. I was reading up on the treaty and learned the history behind Hammerfell and their fight against the Aldmeri without help from the Empire.
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