Well, I'd guess its a little like the Cold War... which obviously wouldn't be something you'd know about, so that reference would make no sense so let's pretend I never made it.

[Pepper's fair skin is really quite excellent at letting the entire world know when she's got colour rising in her cheeks. She coughs once, pats at her hair, and moves on resolutely.]

I can't speak to what's actually said inside the domes, but various nation-states in my own world's history have used the constant threat of an attack from the outside to keep their citizens under control and marching in step. At one point, the threat was real enough that they retreated behind the domes, and once the domes were up, the common people would be unable to get information about the outside world directly.