A ruler's primary title is the top tier title which they most identify with.
A ruler with multiple top tier titles can switch the primary title at any time. This is true even for counts, who are not required to use their capital as their primary title. Viceroys and nomads are not allowed to change their primary title (but see below for nomad exploits).
Importance of the primary title
- The heir of the primary title is the character you will play as once your current character dies.
- Under gavelkind, the primary title goes to the eldest child. Under elective gavelkind, the primary title goes to the elected character.
- The capital can be moved to the de jure capital of the primary title, even if you have already changed your capital. This is the only way for a merchant republic to change its capital.
- During a regency, a regent whose primary title is within the relevant kingdom or empire may decide to lower crown authority of the kingdom/empire (without Conclave). This can only happen once to each liege.
- De jure vassals under your primary title (one tier below) will not have the "desires <title>" opinion penalty. As such, when holding two or more titles of the same tier, making the title with the most de jure vassals the primary title can cut down significantly on discontent among your vassals. This is more significant if you have a titular title; making another title of the same tier (with de jure vassals) the primary title is advised. Note that titles containing the realm capital are also exempt from "desires <title>".
- Newly created kingdoms and empires have their crown laws and succession laws copied from the primary title.
- Crown laws of the primary title are applied in some outlying areas.
- The "Fabricate Claim on Liege" plot requires the target title to be a direct de jure liege or vassal of your primary title.
- When offering diplomatic vassalization, the target's primary title determines whether they are a de jure vassal.
- It is not possible to usurp the primary title from a merchant republic.
- After inheriting titles from another realm, the primary title determines which realm the character will be under.
- If inheriting a title of a higher rank, this higher rank title will become the character's new primary title; the character will thus join the other realm as a vassal. If the higher rank title is an independent realm, the character will also become independent, even if the new rank remains lower than that of the former liege.
- If inheriting a title of equal or lower rank, the character's primary title remains unchanged and they remain as a vassal in their current realm.
- If the title inherited is at least of the rank of the top liege, the lord will become independent and will take his previously owned titles along with him in his newly acquired realm. The previous top-rank liege will get a strong claim on all titles that left his realm.
- De jure shift will assimilate titles into the primary title, and the tier of the primary title determines the titles which can be assimilated. (Empires can only assimilate kingdoms, while kingdoms can only assimilate duchies.) However, duchies can also assimilate other duchies, making de jure shift possible even without a kingdom-tier primary title.
How to change primary title as a nomad
Nomads cannot change their primary title directly. This may be troublesome for khagans hoping to use the "Restore the Roman Empire" decision. However, a nomadic clan may gain another empire as primary by pursuing an intergenerational strategy.
Ensure that at least one son of yours is an eligible heir (adult and same culture) and would be the second in line to inherit. (He must have less prestige than your heir, be an eligible heir of your heir - that is, an uncle, brother, son or nephew - and have the most prestige of all your heir's heirs.) You can increase his monthly prestige gain by giving out a honorary title, a council position or a commander position, or lower his prestige directly by making him marry a low-status woman.
Weaken your vassal clans, so it's easy to regain your old titles later. Usually, you should have the maximum number of possible clans, with all of them holding only one county, nomadic or not. (There's no risk of minor clan uprisings once the maximum number of clans has been established, and the clans themselves will be too weak to rebel on their own.) In this case, however, there still needs to be one clan that would rebel if you tried to absorb it.
Attempt to absorb a clan that would rebel if you tried, and immediately surrender to their demands. You will be killed, and will lose the title of khagan as well as your other imperial title(s) to the rebellious clan leader, becoming one of his vassal khans. Crucially, your new heir - but not you personally, for whatever reason - now has strong claims on your former imperial titles, since he is the son of the former khagan, while you still hold all land the former khagan held. Transfer control to this heir by whatever means you like, e.g. forcing an abdication by surrendering to a feudal vassal's rebellion.
Now, if you press your claim for a single imperial title against the khagan, it will become your primary title, since khans are only king-level; this should be a very easy war if you weakened your clans as advised. Your primary title will stay the same even if you also press your claim on your old khaganate afterwards to regain all of your former territory.
With the Jade Dragon DLC, there is another, fairly easy, way to change primary title as a nomad, as long as you have at least one king title in addition to the khanate title. It is best to absorb all your vassal clans before attempting this strategy, as they will all break free if you do not.
Declare an invasion war on China, then immediately surrender. When the news event about your surrender pops up, do not dismiss it. Surrendering causes your khaganate title to shatter, (freeing all your vassal khans in the process) leaving you as an independent king-tier ruler. If one day passes, the game will realize that you are and independent nomad and recreate the khaganate title. However, during the one day that your empire is shattered, you can create any empire title and it will become your primary title.