The setting hasn't changed at all since Divergent. We asked enough questions about the setting of Divergent to top an extra-large deep-dish pizza: Is it, like, 20 years in the future? 200? Is there a disaster outside the city? If so, we choose—well, can we choose to be Divergent?
Insurgent answers none of these questions. The factions are too busy warring against themselves to even think about why they might be in the situation they're in. The characters still don't know they're in the city of Chicago, and they don't know what's outside the city. The only clue we get is when Marcus says "We are not from here, Beatrice. We were all placed here, for a specific purpose" (37.102). So maybe the world isn't totally a wasteland outside the city?
All we see during Insurgent are the various faction headquarters and the dormitories, cafeterias, and bathrooms inside them. Seriously, almost every scene takes place inside a dorm room, a cafeteria, or a bathroom. It's enough to make us fear that the worst part of a post-apocalyptic society isn't the mind-altering serums; it's the fact that high school never ends.