Allegiant reveals that everything we've read in Divergent and Insurgent is the result of a nationwide genetic experiment. See, scientists isolated a "murder gene" (15.15) and removed it, "editing" (15.18) humanity as if we were all hip-hop albums being sold at Wal-Mart. This experiment failed, as these things always do in science fiction: "Take away someone's fear, or low intelligence, or dishonesty… and you take away their compassion" (15.22).
The result was the Purity War, in which most of America was destroyed. We're not sure how, but we do know it was grisly. So, in an effort to rebuild society and cure all this genetic damage, people were put in various cities (like Chicago), fenced off, and left to reproduce like genetically damaged bunnies until the genes fit right into place once again. Those people are called Divergent.
Being experiments themselves, Tris and Tobias are kind of dumbfounded that all of this has been going on behind the scenes. "It's like they just arbitrarily decided that one kind of DNA was bad and the other was good" (24.21). Great. Just what we need: more genetic superiority that reminds us of the Nazis and eugenics.
The Bureau blames everything on genetic damage: "In reality [the genetically damaged are] poorer, more likely to be convicted of crimes, less likely to be hired for good jobs…" (23.89). It creates kind of a chicken-or-egg situation. Does genetic damage cause poverty, or does poverty make people act as though they're damaged?
Tris finds herself believing that people are people, no matter what their genes say about them. She thinks that societal factors, not genetic factors, affect human behavior, and the whole genetic thing is a cop-out: "Some of the people here want to blame genetic damage for everything […] It's easier for them to accept than the truth, which is that they can't know everything about people and why they act the way they do" (22.51).
We're not sure if there's an easy answer to this dilemma. Tris ends up taking the easy out and erasing everyone's memory so that they forget the whole genetic damage issue altogether. Us? We think we agree with Matthew, who says, "If everyone would just keep learning about the world around them, they would have far fewer problems" (22.55).