All principalities are governed either by a single ruler assisted by his appointed ministers or by a ruler and the hereditary nobles who hold power in their own right and have the loyalty of their subjects.
The Turkish sultan divides his kingdom into districts that are managed by his administrators, but the king of France has to contend with many lords who have longstanding privileges. Because the sultan's administrators are dependent on him for their power, they are not likely to help a foreign invader. But if an invader had a strong enough army to win, it would be easy to keep their territory, because the people are not personally loyal to the administrators. In a kingdom like France, the nobles are always ambitious and ready to turn against the king. But if they assist you in conquering the country, they will also be ready to turn on you. Even if you kill all the royal family, the nobles remain, and you can neither satisfy them nor get rid of them. Whether one can control a territory depends less on personal ability than on the character of the territory.
If the conquered territory was formerly a republic, in which the citizens were used to living under their own laws, you must destroy it, go live in it, or let the citizens live under their own laws with a government that is friendly to you. If you do not destroy the city, it will destroy you, so fiercely will the citizens remember and long for their freedom.
