Advanced Order Control is the internal name for XC's unique government system.
Working along with the culture system it allows each region to be shaped towards a full factional control, a protectorate-like system or in some cases a mixed administration.
What makes it unique is its capability to self-destruct upon conquest by a foreign culture.
This means that for example a gallic horde conquers Rome they won't be able to build up straight away but instead will have to rebuild the government and possibily migrate some of their own population in order to "celticize" the region.
You will only be able to retain the original government infrastructure if a friendly culture is already present in the settlement, in which case the government will not self-destruct.
As shown by the tree, the government level influences the type of military (and infrastructure) development available in the settlement.
-Choosing an allied governemnt will turn it into a de-facto protectorate that will allow you to build high-level auxiliary barracks at the expense of some economic impact (the native ruling class will keep part of the income) and the ability to train factional troops.
- Going towards regional pacification will instead open up colonization and lead the road to fully developed factional control, unless you choose to allow a mixed-style governmnt (supervised native administration) which will bar the more advanced troops but allow a relatively balanced mix of factional and local troops.
If you want to control fully the place you will need to move some of your loyal subjects through building a colony level, which will both give an anchor to your factional government to develop and allow progressively higher factional barracks.
Failing to do so will result in your control attempt collapsing and you will need to rebuild your government from scratch.