Expanding your realm is a primary goal for most players and for ambitious AI characters.
There are many ways to gain territory in Crusader Kings II. Some give you territory personally, while others give you new vassals or expand your vassals' sub-realms.
Warfare
- Main articles: Warfare, Casus Belli
Many CBs, such as Holy Wars and personal claims, expand your realm directly.
获得宣称者
- Main article: Claims
When viewing a title, clicking the "show claimants" button will display a list of all claim holders, together with an icon indicating whether they will accept an invitation to your court. Note that this display does not distinguish between strong and weak claimants, nor does it show characters who will get claims upon the deaths of their parents but do not presently have them.
It is difficult, but usually possible, to gain claimants on infidel kingdoms. If a claimant resides in a mere county, you can vassalize them with a de jure war, a Buddhist minor holy war, Muslim holy war. The Force Vassalization CB can vassalize an entire small realm. If you capture a child in siege or sack, you can educate them into your religion after moving them from a dungeon cell to house arrest, and then release and invite them upon adulthood.
With 
Conclave DLC, favors create other opportunities to gain control of claimants. Some claimants might be susceptible to invitation by favor, as long as they are not councilors or close relatives of their liege. Young claimants can be invited normally after using a favor to educate them into your religion. Female claimants can be gained by using a favor to arrange a betrothal/marriage with one of your kinsmen.
Pressing claims for others
- Main article: Claim wars
You must land the claimant before enforcing demands, unless the claimant is of your dynasty or the target title is a de jure vassal of yours. Granting a county is the most common, but you can also grant a barony-level title. You can even use cities or temples, if you don't mind having vassals of a different government. Keep in mind that you can only grant secular titles to unlanded women if you have absolute cognatic succession law, or theocracies to unlanded women if your religion allows female temple holders.
Because landing claimants depletes your demesne, you must complement claim wars with religious wars, title revocation, or use of the "Revoke Vassal Title" plot (perhaps against the very vassal you just got a second county for).
Activating weak claims
| Situation that activates a weak claim | Strategies |
|---|---|
| The title holder is female and the claimant is male |
|
| The title holder is in regency |
|
| The title is currently contested in another war |
|
| Claimant is 2nd or 3rd in line to the title |
|
Religious wars
- Main article: Holy War
If you can gain a border with a region of disorganized infidels, you may be able to conquer the entire region through a series of holy wars. Coreligionists are likely to join in defense against a holy war, so attack when (1) you can win quickly through assaults, (2) their coreligionists are distracted, or (3) you can declare simultaneous wars against many of them. Smaller "religious" wars, such as County Conquest (Pagan), do not allow non-allies to join.
Some religions have access to powerful CBs that allow followers to conquer or invade entire kingdoms. If you want access to these CBs, consider converting. Note that the Tribal Invasion CB is unlocked through a combination of religion and culture.
Arranging for vassals to inherit foreign territory
- Main articles: Inheritance conflict, Invite to court
If a vassal inherits an equal or lower ranked title from outside your realm, your realm will grow correspondingly larger. For example, if you are a king, invite heirs to large foreign duchies and grant them local duchies.
Heirs are extremely valuable, so you should not hesitate to use every trick at your disposal to make them accept an invitation to your court. Bribe them, let them educate your children for a week, or use any other method of increasing their opinion of you.
While this is one of the fastest ways to expand (especially at king/emperor rank), it comes with some warnings:
- The strategy can backfire:
- If your vassal inherits a higher ranked title than what they are holding, your realm will shrink instead! (Depending on the new primary title, your former vassal will either be independent or be part of another realm.)
- If your vassal dies without children, the title may be inherited by their parent! (This becomes a problem if it leads to the first point.)
- You should receive a "Vassal Inheritance Warning" if a backfire scenario is possible.
- This can result in powerful vassals who may not be loyal to your heir.
- If their former liege is at war, your vassal's liege levy may be considered "raised". You will not be able to raise any levies from them until their former liege is at peace (or the unit is obliterated).
- Their former liege will gain claims—but only on their former vassal's demesne titles, not on all land that leaves their realm.
- Female heirs are trickier to land. The order in which they and their husband die can influence the final liege of their child. The child will ultimately follow the higher title; if the titles are equal, they will stay with the realm that landed them first. You should receive a Vassal Inheritance Warning if this is a possibility.
- Some titles cannot be stolen this way:
- The other realm may have crown laws that prohibit titles from passing from the realm through inheritance.
- Merchant republics cannot be inherited by other rulers.
- The "heir" shown in a ruler's portrait screen may be misleading.
- With gavelkind, siblings might inherit other titles. Use the same gavelkind strategies you would use for your own children.
- With feudal elective or tanistry, the heir may change!
- With feudal elective, ensure the "heir" is actually winning the election. When the family is losing, the portrait screen will show a dynastic heir who inherits family lands (e.g. a duchy), rather than the non-dynastic heir who inherits the primary title (e.g. a kingdom).
- With open elective, the fallback when an independent feudal ruler has no family, the "heir" will cease to be heir upon joining your court!
Several map modes are especially helpful here:
- Direct vassals (or Ctrl+clicking in Independent Realms mode) can help you find the largest de facto duchies in foreign kingdoms.
- De jure kingdoms has a hover tooltip showing the laws relevant to out-of-realm inheritance.
Diplomatic vassalization
- Main article: Offer vassalization
A same-religion ruler may agree to become your vassal if at least two of these are true:
- You have the same culture
- You are two ranks higher
- You are their de jure liege
You can often do this after forming a kingdom where the de jure rulers are weak and culturally homogenous. Examples in 867 include Ireland, England, and Sweden.
Diplomatic vassalization can be used to vassalize mercenaries and holy orders.
Gaining liege titles
- Main article: Playing as a vassal
If you rule a small independent realm, consider swearing fealty to a higher-rank realm. This will give you protection from attackers, letting you focus on offense. It will also let you attack your new fellow vassals (unless under medium crown authority), and give you opportunities to seize the realm from within.
A count vassal of a king can request the duchy in which they reside. Each character can only use this decision once, even with a new liege, so you should only use it when your liege thinks highly of you (50+) and does not have the greedy trait.
You can use the "Fabricate Claim on Liege" plot if you are a direct de jure vassal. Alternatively, you can form a faction for elective succession. Once you are a claimant or your liege uses elective succession, you can form a faction to place yourself on the throne. The intrigue focus and favors can help you gain faction members even if the liege is popular.
Marriage
- Main articles: Marriage, Advanced marriage guide
Marry title holders, heirs, or characters who can be made heirs by assassinating others in the line of succession. If a parent won't let you arrange a marriage, try inviting the potential spouse instead.
After you and your spouse both die, your shared heir will inherit both titles. In addition, you will have an ally who always accepts your calls to arms.
In case your spouse dies first, keep in mind that your heir is no different from anyone else when it comes to determining what titles are in your realm: your heir will cease to be your vassal upon inheriting a higher title than he already holds.
Check the succession law of the target realm: a spouse with Feudal Elective may try to elect a dynast rather than your shared children. If you fail to inherit the realm, you will at least get a claim.
Encouraging vassals to expand externally
(Without Conclave) Your vassals can expand for you by attacking external realms, so long as crown authority is not at Max. Thus, you may want your most powerful and ambitious vassals to share borders with weak foreign realms.
You can help them out by:
- joining (taking over) their war
- declaring another war on the same target, perhaps with a different cause belli (so you and your vassal each take a part of the targeted realm)
- sending them one or more extra gifts of gold
- constructing buildings in their sub-realms. Constructing directly in their demesne will increase their opinion of you for a while.
Raising crown authority to Medium prevents dukes from expanding within your realm, which should encourage them to focus on external expansion. On the other hand, it may decrease the number of troops your vassals have.
With Conclave, preventing internal wars requires Imperial Administration.
Caveats
If you're looking to expand your realm, knowing what actions do and don't expand your realm is vital. It can be frustrating to push a claim only to find that the county isn't added to your territory when you win the war.
Things that never put titles in your realm:
- Allowing any character to get a title equal to or higher ranked than your own. For example, a duke (including doges and petty kings) cannot be the liege of another duke. Even if he was landed before he got the new title, he will become independent and take all his land with him. It may be worth pushing such claims anyway if they belong to your heir, since, if your heir outlives you, you will eventually play as him and have his titles.
- A courtier inheriting a title. This includes members of your dynasty, even heirs! They will instead become independent of you, and might even become the vassal of another realm (Remember: the vassal contract follows the primary title). Landed people are by definition not courtiers, so if the title is lower than your own rank, simply land the courtier with a title equal to what they will inherit, and you will remain their liege. Alternatively, check the title and culture of the courtier; if the courtier will agree to diplomatic vassalization after inheritance, you need not land the courtier.
Other considerations
Focus on increasing your rank
Going from duke to king allows you to have dukes as vassals, greatly speeding up your expansion rate. If you can't create any de jure kingdoms near where you started, try to unite Ireland (or any other small kingdom) instead.
It may also be possible to create a titular title if you hold its capital. First check the list of createable titular titles. If it has been 100 years since your start date, some kingdoms may have become titular due to their duchies being assimilated into other kingdoms.
The 
Charlemagne DLC allows you to create a new custom kingdom or empire if you are independent and have a large enough realm.
Expand within the de jure empire of your capital
Due to de jure modifiers, it is less worthwhile for you to expand beyond your de jure empire. An exception is to ensure de jure drift, be it of a neighbouring duchy into a kingdom controlled by you or your vassal (better if it's your kingdom), or even a neighbouring kingdom into your empire.
Another exception is if the player is aiming to form either the Roman Empire or India; both empires have many de jure provinces which are outside the borders of its constituent empires.
Spread your dynasty
It can be worthwhile to get other realms under control of your dynasty, even if they are not your vassals.
- They will contribute to your dynasty prestige.
- They are often willing to be allies.
- Future claimants will be of your dynasty, so you will not have to grant them land when pressing their claims.
- Rulers will let you marry their daughters (or matrilineally marry their sons), because they are no longer concerned about non-dynastic succession.
Avoid angering infidels
Avoid getting within Holy War range of powerful infidels until you are ready. However, when you do declare holy wars, consider declaring many wars at once, so that they can't join each others' wars.
If you are not Christian, avoid unlocking the crusades early. Conquering "canary provinces" such as Toulouse or Braunschweig will allow crusades to begin before 1090 and will cause Catholic holy orders to be created. On the flip side, if you are confident of facing the wrath of frequent crusades, they are a good source of wealth, piety, moral authority and decadence reduction (for Muslims).
Summary
To expand your realm:
- Push any claim where your character is the claimant.
- Generally, push others' claims only if the claimed title is a lower rank than your primary title and the claimant is landed or in your dynasty.
- But push any claim for your spouse, parent, heir, or heir's spouse, with the understanding that higher-level titles will not be in your realm until you are playing as a character who has inherited it.
- Marry your father, yourself, or your heir to people with desirable titles or who are heirs to such titles, with the understanding that the title won't be in your realm until you're playing as a character who has inherited it.
- If marrying an heir, try to kill the current title holder, which will ensure the heir will not change before the current heir gets the title.
- Give titles to foreign heirs, and make sure they inherit the foreign territory rather than the other way around.
In addition, you can also expand your realm by taking advantage of certain CBs, such as subjugation, invasion, and holy wars, but not every CB will give you an opportunity to expand your realm, so pay attention to what exactly you stand to gain by fighting the war.