Assume the existence of an organized state that spans the entire world known to it, or at least as much of the world as it can interact with. This could be a global empire. It could just as easily be a colony planet cut off by decades of communication time and centuries of travel time, or an island people who have lost the ability to build ocean-going ships. I am not talking about isolationist states - those that have chosen not to interact. I am limiting myself to states that do not border any populated areas, where if there are any other civilizations in existence, it is not technically feasible to trade or make war with them.
What would the internal politics be like of a state with no external relations? How are they affected by, for example, having nobody to compare themselves against? There are no outsiders to demonize, no outside threats you can rally the people against. There are no other states to look at as examples of political systems, so all currents of political thought must come from within the system (that may not be a significant limitation) and there's no way to see how policies work without trying them yourself.
Please do not use this question as a place to dispute the feasibility of "I am the king of all I survey" situations. If you want to do that, ask another question.
I have seen What would happen to a human Galapagos? That question and its answers focus on culture and biology. I'm asking strictly about politics.
What would the impact of a global and unchallenged empire be on world history? is closer, but it focuses too much on an empire (I'm also looking for answers pertaining to non-autocratic states) and on how the government maintains control. I'm assuming that it does and looking beyond that. I'm looking for more subtle things like "What sorts of political parties are more or less likely to form?" "How would the economy of an industrial state be affected by the lack of foreign exchange?"