The idea of a city split into two by ideologically opposing factions, and the split being marked by a big wall, sounds like sci-fi now. Also, the idea that a physical barrier could affect the spread of information. Its interesting how much of 20th century history centers on Berlin. There's a wall museum in Berlin, well worth visiting. Edit: thanks for the reminders about contemporary split cities, sobering to think a…
Sci-fi is usually about future. With 8 billion people in the world and growing, I can definitely see some other places divided by walls so that hostile factions do not mix.
There are "peace lines" in contemporary Belfast and Derry still in existence.