If you hate the Thalmor like all right-thinking Skyrim players, here's a mod for you. Assault on Valenwood ends the treaty between the high elf supremacists and the Empire, and lets you join the Imperial Legion in a war for the province of Valenwood. You'll be supported by some of the local wood elves and khajiit as well while you take the province back city by city.
It builds on the previous Valenwood mod, taking that huge map and adding a series of battles across it. Note that you don't need the original mod to use this one, though you will need Skyrim Special Edition version 1.5.73 or higher and, as modder theblackfist warns, "a bunch of followers to help you and your allies out" and "A LOT OF POTIONS".
To begin Assault on Valenwood, travel to the Solitude docks and find a ship called The Avenger. Find the trap door on board, open it, and enjoy your time in the Imperial Navy.