 Mill thinks that it is impossible to find a single set of institutions that is progressive for all times and places.  The most that we can do is to specify what institutions are best for societies at a given level of civilization.  Mill controversially argues that despotic governments may push “barbarians” to the next level of civilization (1859, 14–15). But Mill argues that in more advanced societies, free institutions promote further progress.  They do so by allowing ideological conflict, which is a powerful engine of ideological development.  Mill worries about the transition from one set of institutions to another.  Civilizations can reach a certain level of development and then stagnate because they do not undergo institutional change (1861a, 234–5). 