You can start as a duke, vying for power among other vassals under a king, or as the king himself, trying to manage your vassals and keep it all from falling apart. War is a function of politics in CK2 it exists mostly to claim what is “rightfully” yours or to prevent that from happening to you. This time it has been a lot more fun, but I do have some comments on the game: Recently, I reinstalled it and gave it another try.
I couldn’t get into it, then uninstalled it.
I bought Crusader Kings 2 with some DLC about a year ago as part of a Humble Bundle sale, and tried it.