Our first topic of discussion was proposed by fencer_x over on tumblr:

dat world buildin’. No.6 is super technologically advanced but No.5 isn’t? Is there no data sharing? Timeline suggests they all abide by the Babylon Treaty to a point sooo?? Does no one else have a problem with No.6 or does no one else know?

I have wondered this, too! In the anime, No.6 seemed to have internet (wasn't Yoming a 'net reporter' or something along those lines) so one would think there's some worldwide communication. (Or at least the capability for it: No.6 might have a big firewall, a la PRC.) 

I think all the city-states are pretty insular (or at least self-sufficient), so it's probably a scenario where not all information is being shared with other city-states (like, you know, the part where No.6 is developing weaponry in direct violation of the Babylon Treaty). Who knows what else the Babylon Treaty stipulates apart from 'no warfare or weaponry'? Is there a clause for the prevention of dystopias??

Or you could take a super gritty, darkly realistic view of it and extrapolate from world politics: even when countries know there's shittiness going on outside their borders, the options for resolving the situation are limited and not always effective. But I would err more on the side of outright ignorance, given that No.6 has study abroad programs in partnership with other city-states* for its elite students. (*No.5 at least; maybe everyone else is sanctioning the hell out of No.6 and No.5 is the hold out.)