If you go to the Manage Civilizations tab in the Scenario Editor and click on a province like London, all the different types of Civilizations, like England and the United Kingdom, pop up. Wonder how to add your own civilizations on a province? (No, no game files included!)
How to find it
On the title screen, click on the Editor, Map Editor, the map you're focusing on, then scroll down until you see the button Generate Suggested Civilizations.
What it does
Once you click on it, it will reload the game and find every single scenario you made and find all provinces and see if there is a civilization on that province, then it generates that civilization on that province.
For Example, you put the capital of Ming in Paris and you clicked the button, once it's done loading, you find Ming suggested to you once you click on the province Paris in the scenario editor!