Playing as a vassal
As a vassal, you are protected from outside attacks, but you have additional concerns and duties.
As a vassal, your military is weaker than independent rulers of the same size and rank. Independent rulers get a +50% bonus to levies from the capital, and +25% bonus from their capital duchy if they're a duke or above. As a vassal, you get no bonus levies from your capital as a count, and a reduced bonus of +25% from the capital and +15% from the capital duchy if you're a duke or king. Thus, unless you have other factors in your favor, concentrate on expanding within your liege's realm, especially if you're a vassal count; securing that first duchy title would help you greatly.
As a vassal count, becoming the duke of the duchy your county belongs to is a step up in terms of military power. Beyond that, becoming a grand duke will give a +1 bonus to your demesne limit before modifiers. A grand duke with complete control of the capital duchy is in a relatively strong position for greater ambitions. Of course, before this stage, you might want to settle your succession laws.
As a vassal, if your government type is the only reason why you can (potentially) raid, your liege's government type must allow raiding as well. Vassal tribes who cannot raid due to their culture or religion must have a tribal or nomadic liege in order to raid. Thus, Anglo-Saxon tribes under the Petty Kingdom of Northumbria in 769 cannot raid unless they become independent, but Swedish Pagan tribes under the Catholic king of Sweden in 1066 can raid, provided they stay Pagan. If they convert to Catholicism, then they must become independent in order to raid.
Defending your liege
Sometimes, you may have to raise your own troops to help defend your liege. This is especially important if your titles are at stake and and your contributions would definitely be able to turn the tide decisively in your liege's favor. Battles started with your own troops will not contribute to the war score. As such, you should link your army to your liege's army or join ongoing battles. Alternatively, you can destroy enemy troops and let your liege concentrate on sieging.
You can create or join up to two factions.
If you are the most powerful faction member in the realm, your liege is likely to send their spymaster to scheme in your capital, forcing you to promise never to start factions. Due to a bug(??), you can still join factions even if you have been discouraged from factionalism.
You will be the leader of a faction if you create it, or if you are the most powerful member when the leader quits. Being a faction leader has significant advantages:
- You can judge the best time to send an ultimatum better than AI leaders, and can wage war more effectively.
- You can recruit faction members using the spymaster "Scheme" mission, Intrigue focus, or favors.
- With the latter two methods, you may be able to avoid creating the faction until you are ready, thus avoiding attention from your liege's spymaster. However, there is a risk that someone else will create your preferred faction and you will not be able to lead it.
On the other hand, being a non-leader member lets you double your troop contribution to the revolt. AI leaders may issue an ultimatum whenever faction power is above 75%; you may wish to avoid joining until the power (with yourself included) is around 120%.
AI rulers may fold if faction power is at least 100%, letting you both avoid a costly war. They are more likely to fold at 150%, 200%, and 300% power. They are less likely to fold for each of Strong/Brawny, Brave , Proud , Envious , Greedy , Wroth , or Ambitious . They are more likely to fold with each of the opposite traits. Finally, they are less likely to cave to attempts to usurp their titles.
With Conclave activated, being a council member may prevent you from joining factions. You can resign your position if this is a problem.
War against a liege
Any war against your liege will mark you as "in revolt", preventing you from declaring other wars. Some wars, including all faction wars, also give you a "temporary title" of the same tier as your liege. While you hold a temporary title, most diplomatic interactions are disabled.
Some wars can be directly declared against a liege, without using a faction. Notable among these are:
- Press claim, which uses the faction version of the CB, giving you a temporary title
- Press all claims, which does not give you a temporary title
- Independence (see link for differences from the faction version)
- Decadence usurpation
Unlike sending a faction ultimatum, declaring war on your liege does not require being at peace. This makes it more feasible to build external alliances before going to war with your liege.
Gaining liege titles
A count vassal of a king or emperor 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.
Taking over your liege's main title is a more difficult process. There are several possible approaches.
You can use the "Fabricate Claim on Liege" plot if you are a direct de jure vassal. Once a claimant, you can form a faction to place yourself on the throne. These actions are most likely to succeed under a new, unpopular liege. You can also get a claim by marrying into the liege's line, since children inherit claims from both their parents. Make sure the person you marry will get an inheritable claim - generally, children of rulers get inheritable claim but grandchildren don't. If you manage to dispose of all other potential heirs to the throne, you can inherit it directly without needing to go to war. Finally, the pope can grant you a claim on a duchy if he dislikes the current duke and likes you.
Alternatively, if the realm has elective succession you can become king even without a claim. You can be elected peacefully if the other electors like you much more than your liege's heir. You can also start a faction to put yourself on the throne. If your realm has another form of succession, you can start a faction to switch it to elective.
With the Conclave DLC, you can also use the more powerful "Oust Ruler" faction. If you are the "most popular vassal" (by average opinion?), this makes you king or queen in one step. If not, you can immediately faction against the installed ruler, since you only have a truce with the previous ruler.
Finally, you can become king if you manage to expand your holdings to the point that you directly control the majority of the de jure territory in the realm. Declare war with the Independence casus belli or using an Independence faction. Once independent, you can usurp your liege's title. Note that this won't transfer control of your former liege's other vassals to you, but they'll be likely to accept peaceful vassalization requests.
Joining the council
Being a council member gives you a small amount of monthly prestige and income, and doubles your plot power against your liege.
Without Conclave, you can gain +1 in the relevant skill when you become a councilor. Simply select the appropriate "become councilor" ambition when your liege offers you a position. (If you already have an ambition, but have had it for 3 years, you can cancel it to choose a new one.)
Do not become Marshal if you have the wroth trait. Similarly (but only without Conclave), do not become Steward if you have the greedy trait. You could be accused of a crime that allows your liege to confiscate your entire treasury.
To assign yourself a ward while you are a councilor, you must make an "educate child" request of your liege. You must resign from the council in order to arrange a marriage for yourself.
Crown authority decreases your available demesne levies by 20% per level, effectively forcing you to leave some levy troops as extra garrison. But it also applies to your vassals: if you are a duke, crown authority forces counts to provide troops even if they dislike you.
After any succession, other vassals are likely to join factions to lower crown authority -- especially if crown authority is already high, and especially if they are not inclined to join an independence faction instead. You probably want to lead this faction: you can choose whether to issue an ultimatum (depending on what you think of the CA level), and you control when and how it fights. However, if you are powerful enough, you could join the faction as a member and contribute both temporary-liege levies and personal levies.
A guaranteed way to lower crown authority is to present an ultimatum during a regency. The regent will always force the ruler to cave, even if the faction is pitifully weak.
If you intend to carve out your realm while remaining within your liege's, lowering CA to below Medium is crucial as Medium CA disables wars between vassals.
Having your titles revoked
Your liege is likely to revoke your titles if:
- Actively dislikes you (-25 or worse?) and has a valid reason, or
- Views you as an infidel (even without Religious Control law), or
- Revoking the de jure capital of their primary title, or possibly the duchy that contains it
Lowering your opinion of your liege
When your opinion of your liege is low, you can escape paying taxes or paying for liege levy maintenance. Having a low opinion is also a prerequisite for the "fabricate claim on liege title" plot (depending on traits). However, if the low opinion goes both ways, you may run the risk of having your titles revoked.
- Convert to another religion and become zealous (one-way; if your liege is of a different religion and zealous, be careful!)
- Convert to another culture (two-way)
- Become ambitious and activate ambition opinion (one-way)
- Take on traits that conflict with your liege's traits (mostly one-way)
- Join a faction and wait for your liege's spymaster to force you to stop (-10 opinion: "Discouraged from Factionalism") (one-way)
- Reduce general vassal opinion: Assassinate your liege or liege's chancellor; excommunicate your liege if possible; Byzantine emperors and Catholic emperors who have the Pope as a vassal are immune. (one-way)
- If Conclave is activated, refuse a seat on your liege's council if you qualify as a "powerful vassal" (one-way). This also allows you to join factions freely if you are non-tribal or non-nomadic.