After the Dome Fortresses were launched, it wasn't all milk and honey for the rest of mankind. First, there was the challenge and problem of overpopulation. The fortress was large, but it was impossible for it to accommodate even a significant portion of the Earth's population.
This led to 'The Grazing,' where part of humanity was forced and abandoned outside the walls to die. This resulted in the current Outsiders, such as the Ntuli people, and where their hatred stemmed from.
Even then, mass population was still an issue. So the Fortress of Allan Fort adopted a feudal system, comprised of hierarchical societies, by adopting various forms of social stratification similar to those formerly used on Earth during certain time periods.