Just to be sure, you are playing with a Roman faction?
It seems that your standing with the people is too low, and your standing with the Senate is too high. It is my understanding that Senate standing must be 1 or else it will not trigger.
Keep taking over more territories would be the quickest way to trigger the Civil War. Build up your forces in Italy and where you neighbour other Roman factions too in the meantime. Also, do not carry out Senate missions as this will upset them and drive your standing further down.
It wil trigger eventually!
Laws are a tedious business and counting coppers is worse
Im playing with Bruitii. I have all of Greece, Macedonia, Dacia, a large chunk of the Middle East and most islands.
On my second run, 30 provinces and still didnt trigger. I conquered faster now, I have 8 with the people but for some reason the Senate loves me as well (8). Im sending assassins against the senate members now, but they never get caught, no matter how bad.
In one of my Scippii games it didn't trigger until I had almost surrounded the other romans. I controlled africa, the middle-east, spain, gaul, britain, a few greek cities and I was starting to push into turkey.
"How the Christ do you expect to reverse-Atlantis an entire city? You're just the Dragonborn, not the Daedric Prince of Civil Engineering." - DocWily