User blog comment:Thedoucheinthenorth/A question of morality/@comment-68.20.166.62-20121213204901/@comment-3472264-20121222215140

Dude it's not that hard to understand. Dominion wants to rule Tamriel, Empire rules Tamriel. The quickest way to take over something is to destroy the ones who currently control it (E.g the Empire). So obviously since the Dominion wants to rule Tamriel the first step would be to destroy the Empire hence you have The Great War and the capturing and retaking of the Imperial City.