I haven't gotten around to adding that to the codex yet. But, you basically have city-states and Nexus Industries. If a city can manage on its own, then it becomes an independent government ruled by a 'Regent'. They run the cities as they see fit and usually have their own security forces.

The army is the only institution of the old government that existed before the Mordrem, therefore also independent. They don't answer to Nexus Industries or any city-state. However, they also don't care about politics in the same sense as say, city-states.

That leaves Nexus Industries as the de facto world government outside of city-states, to some extent. Nexus has their own elite army, but they don't care about protecting regions or anything other than their own interests, which are basically Gaia extraction, Mordrem research, and displacement experimentation.