if i may contribute to this discussion, here are my 2 cents on this issue:
new imperial titles should be creatable, but not be de iure
i argue for this point not because i am concerned about historicity. Rather, i argue for this point because, while having an 'empire of brittania' and 'empire of scandinavia' can be useful if you focus your conquests in these regions, there are many situations wherein it would not make sense.
For example: Suppose you, the player, were to start a game as harald hadrada, king of norway, and proceed to win the war against harold godwinson, thus pressing your claim on his throne, you would become king of norway and england. Following that, you proceed to invade and conquer the regions of wales and scotland, and crown yourself kings of these two lands as well. At this point, you would be able to crown yourself emperor- but crowning yourself 'emperor of britain' makes no sense. You, harald hadrada (or possibly a descendant at this point) are a norwegian. Your power base is in norway. Why would you crown yourself 'emperor of britain'? It makes no sense.
Instead, i propose the following mechanic. The title of 'emperor' can be claimed if you possess the following: At least 3 kingdom titles, at least 5000 prestige, a large amount of gold and piety, and the pope must have a better opinion of you than he has of the current reigning emperor. Doing so will grant you a title based on your primary kingdom title, such as 'emperor of norway'; possibly with unique decisions for 'emperor of spain' or any other region you wish to specify.
The '3 kingdom titles' requirement ensures that the player has a sufficiently large power base to make a proper claim to the title. The '5000 prestige' requirement ensures that these kingdom titles are not some piddly little backwater lands with few regions. The gold and piety requirements should be self explanatory, as these are used every time a duchy or kingdom is created. Finally, the pope's favour is needed in order to get papal backing for your claim, which sets your claim apart from other 'wannabe emperors' and gives it legitimacy.
This decision should be visible from the start, under the decisions tab, so that players can see it from the beginning. This will allow you to overcome the problem of new players not having anything to aim for, which, i believe, was the reason behind making the titles de iure in the first place.
upon claiming the title
so, suppose you have the requisite number of crowns for your decision. Your character is sufficiently prestigious, you have the gold and piety to spend, and you even secured the pope's backing. Great! You are now an emperor. Unfortunately, the
other emperor, who was there first, is not going to take your claim lying down.
Upon claiming the title of 'emperor' and being elevated to imperial status, the region would be plunged into an 'imperial crisis'. Both emperors get the 'imperial crisis' casus belli on each other. The terms of the casus belli are as follows:
-the empire of the losing party will be dismantled. The imperial title, however, will still keep whatever de iure lands it has, so as to allow the hre to make a comeback if it gets dismantled.
-the losing party will pay a large indemnity to the victor.
-the losing party will lose a large amount of prestige, while the winning party will gain a large amount.
-the losing character may not make a bid for emperor again as long as he lives. (his descendants, however, can.)
while the imperial crisis is in effect (not the war, just the state of two empires of the same religion existing simultaneously), both emperors will receive a harsh modifier (imperial pretender) reducing their prestige. The newly crowned emperor, for being a newcomer to the imperial stage, and not defeating the old emperor, and for the old emperor, for not putting down this pretender to their crown. The imperial pretender modifier will not be removed until one empire defeats the other. This is to encourage both the player and the ai to settle their dispute once and for all.
after winning the war
congratulations! You are now sole emperor of your religious group. However, you still have a long way to go ahead of you. Unless you happen to be the holy roman emperor, none of your lands will be in your empire title's de iure borders. This, in turn, makes it harder to manage your empire until your many crowns assimilate to it- as it should be, for creating a new empire should not be taken lightly.
Neither should you relax your guard. From time to time, other claimants and other pretenders may appear, proclaiming themselves to be the true successor of rome (in particular, the descendants of the emperor you deposed). You will have to defend your crown against them, or fall and suffer the same fate you once inflicted to the previous empire.
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and thus are my thoughts. I, myself, am closer to the 'historical' crowd, and i think that many of my peers will agree with me when i say that it is not the idea of having ahistorical empires
itself that we protest; but that if such an empire is created, there must be a 'realistic' reaction to it (for lack of a better term). Two states claiming to be the successor of the same half of the roman empire should not be able to live in peace, and such a situation should lead to strife and warring, until one or the other is destroyed.
With such a framework, i believe us historical gamers will be satisfied (though i do not claim to speak for all), as would those who prefer a looser interpretation of history. And more than anything, the inclusion of proper mechanics to simulate the circumstances that would accompany the claiming of a second imperial crown would greatly enrich and improve the experience of playing this game.