In my world all I think is important to the question is the existence of thousands of small village to town sized communities. The dilemma is that about five of these are very advanced compared to the others and I don't want them enslaving or enlightening others. So how would I do this?
To make the question less broad I want to limit answers to not be religious or too dependent on past events. So what mindset do the people need for this to work?
This actually happened to a few cultures over history. What tends to happen is that when a culture becomes highly advanced in relation to it's neighbors it can enter a very self-indulgent period of introspection and navel gazing.
Or to put it a better way, their advanced state leaves them disinterested with outsiders. Not xenophobic, just indifferent. China, for example, became so advanced that she was content within her boarders, engaging in philosophical and artistic pursuits.
To make this practical in your world, the outliers would need to be beyond your advanced nation's secure borders and pose no threat. The nation would need to be wealthy and self-sufficient, I.E. have plenty of resources within it's boarders and trade for what it considers luxuries and not necessities.
To prevent a spill-over into your border villages, have them trade with the villages for luxuries, not necessities. The villages would become specialized in making those luxuries and would not be geared towards production of necessities, thus stunting their growth.
You need 'The Prime Directive' and Star Fleet to enforce it -- or their rough equivalents in your world.
Given human nature and human history, I think you need a powerful belief system to deter hegemony by the stronger over the weak. This could be religious, ethical or legal. But whatever the source of the anti-conquest imperative, you'll need a means of enforcing it: religious military orders, ethical wizards or yet something else. Without, some powerful people will tend to prey on the weak.
"dependent on past events" is a pretty broad prohibition, so I apologize if I step on its toes accidentally, but we generally we can look to history for examples of this situation obtaining:
Disease prevents the expansion of one society into another area. This is thought to be a contributing factor to the inability of Europeans to colonize Africa earlier than they did the Americas, despite being nearer. While North Africa was under the protection of powerful kingdoms, sub-Saharan Africa was still composed of many smaller kingdoms and empires which ought to have been susceptible to European colonial efforts just like the Native Americans in the Americas and the peoples of India.
The smaller civilizations have geographical advantages either isolating or protecting them: Switzerland, Greece, Japan - mountains and oceans protected such small nations in the presence of larger aggressors.
Military advantages can tip the scales in some cases. It would be difficult to imagine any argument which would show the Greeks to have been technologically or economically more advanced than their larger Persian adversaries, but typically the Greeks were able to resist Persian incursions because of Greek warrior culture and tactics, which were well-suited to the terrain on which they typically chose to face the Persians (broken ground and enclosed seas).
The smaller states are confederated against the larger states. Despite being more advanced and sophisticated, it was not easy for the Ottoman Empire to conquer Europe because the many smaller states of Europe were generally allied against their efforts. Similarly, the Iroqois were one of the few native american civilizations able to resist European incurions for quite some time because they were confederated and supported each other, offering Europeans no way to turn them on each other.
There's no economic incentive whatsoever. The Bedouin, the Tupi, the various states whose names I can't remember from Afghanistan - these peoples existed on the margins as larger empires around them rose and fell - because basically the cost of imposing hegemony over the regions they lived in was not worth it. There was nothing in those places empires needed for a long, long time. Once you find oil in those places, they are suddenly under threat from larger neighbors.
A major reason that the very well equipped US military failed to dominate North Vietnam was because of dense forests, and a hostile native population (obviously the full picture is much more complicated than that).
A major reason this same institution (now much more advanced) is still largely failing to control Afghanistan is because mountains make war hard for invaders, but not so much for natives.
This same principle allowed ancient Greeks (esp. Spartans and Athenians) to hold out much longer than they otherwise would have against the Persians.
In the end, I think mountains are better, because they make trade hard, as well as conquest. And trade is generally better than conquest for enlightening a population.
I can easily think of a few ways:
1) Democratic society in which the people believe it's bad.
2) The weaker less advanced neighbors all agree to an alliance in the case where the big 'empire' attacks one of them.
3) Nothing worth conquering. The advanced civilization stands for a net loss with nothing to gain to take over others.
Three ideas:
Suppose the advanced towns believe that incorporating the less advanced towns into their societies would "taint" or "mongrelize" or "weaken" their advanced societies.
Suppose they believe that the master has obligations to the slave.
Suppose that the less advanced towns are not "ready" or "smart enough" to be enlightened.
The combination of ideas 1 & 2 could prevent enslavement.
The combination of ideas 1 & 3 could prevent "enlightenment".
Taboos against "treachery" would probably be needed to enforce ideas 1 & 2.
If ostracism is used as a punishment, the ostracized person would need to be prevented from moving to a less advanced town.
