I played Pompejus in his struggle against Caesar. It was a quite easy, but it may have been a bug

A few turns later a "Do you want to stay in the east?" Event triggered.

At least I had all legions, and what I chose at the events didn't seem to have any effect. Well, half a dozen legions in Spain and all the legions of the east made it easy in a war of attrition to bring the Caesarian uprising down.
By the way: Events are a little... strange. In the Severus-scenario (playing as Severus) I chose "accept Albinus as Caesar". The next turn I got the news "War between Severus and Albinus, as Severus denied the title Caesar to Albinus". Ingame there was peace between me and Albinus. Seems the event was wrong connected. (german version).