(Mostly bandit forts, such as Fort Fellhammer on the Pale and Winterhold border, or Treva’s Watch in the Rift).
How to tell that OCW is installed: there will be more flags on the civil war maps. (this description section added with OCW 2.6.1 something to read no matter if you installed this mod freshly new, or it was part of some modpack and you haven’t even seen this description yet) That is so until every hold but the final is yours, then the final hold campaign starts and plays as usual. Moreover, the enemy will attempt to invade your faction holds as well, and you’ll be able to thwart it with a city defense battle.
With this mod, after the first Battle of Whiterun you’ll have to win a city battle in every hold you conquer.
This mod re-creates the civil war quest-line with the original battles, which were cut from the released game.