Stragglers are the largest remnant group after the pandemic and nuclear fallout. They are subsistence level nomads, looking for a means of earning a living.
The Street Gangs have the support of the hegemons, and police the streets by force. Some of the stragglers consider the Street Gangs as thuggish syndicates; it's a title that fits sometimes.
The hegemons compete for ruling interest in the region. They want to monopolize the resources in the area and dictate the way their territories are run.
After the nuclear apocalypse, human survivors retreated behind these enormous walls and fortresses, where they can live in relative peace and safety from the horrors of the outside world.