The Middle Ages is obviously not without Empires. In Medieval Law, usually an Empire was an entity which claimed to be the successor of the Roman Empire. Empires were seen as something above that of Kingdoms, though in CK 1, there was only one true Imperial title, which was the "Emperor of the Byzantine Empire", though this was treated pretty much like a King-tiered title.
Now this title gave an extra bonus that a regular King title did not, which was having an increased desmesne limit.
You could also be crowned Holy Roman Emperor by the Pope (By being King of Germany, Burgundy and Italy at the same time or any 5 king titles AND having good relations with the Papal States), but your character would not gain a title, but a trait confirming that it was Emperor. If I'm not mistaken, all that title gave was a Prestige boost.
Now with CK 2, there is an opportunity to have a 4th tier, which is the Empire itself.
I wonder which Empires did historically exist during the Middle Ages, and what CK 1 King titles (Kudos to Veldmaarschalk for the map) did they encompass?
The ones that I can recall are:
- The Byzantine Empire: a sui generis creation, that is given its own Royal Demesne, going from Albania to Eastern Anatolia which in its full size (discounting owning the whole Roman Empire), was the rightful heir of the whole Eastern Roman Empire, which means it would roughly also encompass Bulgaria, Serbia, Armenia, Syria, Jerusalem and Egypt. Including the Byzantine lands and title itself, 7 King titles would be needed to form this Empire.
- The Holy Roman Empire: Created in the Carolingian period, and after the partitions of its huge Empire, the Holy Roman Empire settled through the duration of the Middle Ages with the territories under the King titles of Germany, Bohemia, Burgundy and Italy. That would be 4 King titles needed to claim this Empire.
- The Empire of all Spains: Created in the 9th century, the Spanish Emperors then embarked into the possibility of establishing Iberian Kings and Emirs as their own vassals, and they were highly treated in the Iberian peninsula at least, as having the Imperial Authority to submit Kings. In this case, it encompasses the King titles of Portugal, León, Castille, Aragón and Navarra. That is 5 King titles.
- The Serbian and Bulgarian Empires: These two were brief empires created by the rulers of the Slav populations which had settled on the borders of the Byzantine Empires and after occupying large tracts of Byzantine European territory, took advantage and increased their legitimacy to that the Imperial tier. Overall, they never managed to overtake enough Byzantine territory to allow them to claim the Byzantine title in CK 1's terms, though the Bulgarian Empire did occupy the territory of Serbia, though that on its own (two King titles) isn't enough in my point of view to make it worthy of having a fourth tier Empire title.
Possible semi-fantasy Empires:
- The Great Britain Empire: Using the United Kingdom as a benchmark, anyone who would possess the King titles of England, Scotland, Wales and Ireland could suffice to declare a 4th tiered Empire of the Great Britain. This would involve having 4 King titles.
- The Empire of Scania: Unifying the Nordic King titles (Denmark, Norway, Sweden and Finland) under a single person would probably suffice for the creation of this Empire. That would be another Empire needing 4 King titles.
- The Cnutian Empire: Putting the same titles as Cnut the Great under the same person, namely Denmark, Norway, England (and then either Wales and Scotland or just Sweden). That would take 4 or 5 King titles needed to create this Empire.
I would however be against stacking Imperial titles, like King ones as these were frequently counter-intuitive (Like Holy Roman Emperor and Byzantine Emperor), since many claim the same lands.
I'm sure there are other real or semi-fantasy Empires that could be viable during this time and I'd like to hear your suggestions.
Summary of possible Empires and needed King titles:
- Byzantine Empire: 7 (Byzantine King title (LOL), Armenia, Bulgaria, Egypt, Jerusalem, Serbia and Syria)
- Holy Roman Empire: 4 (Germany, Burgundy, Bohemia and Italy)
- Spanish Empire: 5 (Castille, Aragón, León, Navarra, Portugal)
- British Empire: 4 (England, Ireland, Scotland, Wales)
- Scandinavian Empire: 4 (Denmark, Finland, Norway and Sweden)
- Cnutian Empire: 4/5 (Denmark, Norway, England and [Sweden or Scotland and Wales])
- Islamic Caliphate: 9 (Arabia, Jerusalem, Syria, Mesopotamia, Persia, Egypt, Africa, Armenia and Mauritania)
- Persian Empire: 5 (Persia, Mesopotamia, Armenia, Syria, Jerusalem)