Both major nations that can be played outside of the campaign (such as Sweden) but also all emergent nations like Poland.

And after beating it with all faction I found out that there is a mod that unlocks all nations in the game. Besides Medieval 2 total war this is the TW game I've played the most. I'm a big fan of Napoleon Total War, the game is everything Empire Total War failed to be, and it is set in one of my favorite eras.