I think of some ways to do it. In another game that I will not name in case it is forbidden to name others (I don't know) there are options to form kingdoms and empires if you dominate a% of them. For example, if on the map of 500 you control Brittany, you capture and keep 75% of France, it would give you the option of calling yourself France, if you keep growing and occupy for example 70% of Western Europe, it would give you the option of calling you Western Europe. This system could be used.
