Slitherine

Does it have something like that - or is it only multiplayer?

As of now there is no campaign system. You can either play against the AI (still not that challenging unless it seriously outnumbers you), hotseat or online against other players. There is now quite a lot of versatility in creating games and with the number of armies it will take a long time to get bored. Note that it is possible to play both sides yourself and I do this sometimes, treating it like any other other solo tabletop wargame.