Well I just got started on my first campaign (Sassanids). I've only played for a few years, so not far into the game yet. My faction starts in a location where there aren't any barbarians nearby, only the ERE, and I got my back comfortably secured by the map edge to boot. The ERE hasn't attacked me yet and I'm not strong enough to attack them either, so it's been just skirmishes with pesky rebels so far. But those romans are massing their troops near my borders, so I guess it's just a matter of time now. They even made peace with Sarmatians and haven't been attacked by barbarians yet making me their sole enemy for the time being.