set up a system where there are three or four 'parallel' societies within the society, each of them at a different stage of this development. the people can move to whichever one they prefer, they can avoid whichever ones are in collapse or decline.  the trick is to make sure the ascendant societies don't feel like they can just conquer the others, and also to make sure that most of the people don't know it is possible to move out of collapsing or declining societies in the system.
Ireland