Marxist theory is about economic conditions and social/political/ideological atmosphere. Marxist theory includes trying to understand the socioeconomic classes within our country. Another part of Marxist theory is about ideology, how it blinds people from the facts, and how it changes the way people see the world. Some ideologies aren't recognized as ideologies, but as a natural way of seeing things. Overall, Marxist theory is mainly about how economics and socioeconomic classes connect and affect each other.
In the Divergent series there is five factions and each one has there own role in their community. However, some have a more important role in their community than others. For example, the Dauntless faction are essentially the military,they provide protection and enforce laws while the Erudite, and Amity faction provide resources, but the Abnegation and Candor faction provide no resources and so they are not vital for the survival of the community, and leads to their factions being attacked. It's the group's resources and importance to the survival of the community that divides them into classes. So Erudite,Dauntless, and Amity would represent the upper, upper middle, and middle class, while Abnegation, Candor, and the faction-less would represent the lower middle,working, and lower class. Each faction also has traits and an ideologies that they expect people in their faction, to conform to. If they fail to conform to the traits and ideology of their faction, they are cast away as faction-less, and must struggle to survive on their own. This pressures people to conform to the ways of their faction and it limits the diversity within their community. In the end the Divergent series shows people divided into groups with different lifestyles, some thrive while others just try to survive, while also trying to change the ways of their repressive society.