Forcing vassalage inCrusader Kings 3is one of the most efficient ways to expand your realm without outright conquest or inheriting claims. Instead of completely absorbing a neighboring ruler’s titles through war and suffering penalties from managing excessive holdings, you can instead make them your vassal and rule over them indirectly. This mechanic becomes especially powerful when used strategically, whether you’re a king, emperor, or even a strong duke. Understanding how to force vassalage effectively can help players grow their domains with minimal internal instability while maximizing their diplomatic and military influence.
Understanding Vassalage in CK3
What Is Vassalage?
In Crusader Kings 3, a vassal is a ruler who holds land and power but is subordinate to a higher liege. As the liege, you benefit from their taxes, levies, and loyalty or disloyalty, depending on their opinion of you. Vassals can range from counts to kings, depending on your own title rank. Forcing someone into vassalage means making them your subordinate through military means instead of negotiation or inheritance.
Why Force Vassalage Instead of Conquest?
While conquest gives you direct control of the land, it can lead to higher tyranny, cultural friction, and domain penalties. Forcing vassalage allows you to:
- Maintain stronger internal stability.
- Expand quickly without micromanaging newly acquired counties.
- Avoid certain penalties associated with holding too many titles.
- Keep powerful rulers in place under your authority, often improving efficiency.
Requirements to Force Vassalage
Rank and Strength Prerequisites
To force vassalage, your character must be at least a king. You cannot use the ‘Force Vassalization’ casus belli (CB) as a count or duke. Additionally, the target must be of lower rank typically a duke or lower for kings, or a king for emperors. You must also have a significant military advantage over the target realm to win the war.
Unlocking the Casus Belli
Force vassalization is not available by default. You must unlock it through the Diplomacy lifestyle, specifically the Befriend tree. The perk required isForced Vassalage, which allows you to use the casus belli on independent rulers. The steps are as follows:
- Choose the Diplomacy lifestyle.
- Progress through the Diplomacy tree, focusing on the August branch.
- Unlock the Forced Vassalage perk to gain access to the CB.
Once unlocked, you can use it on any neighboring independent ruler of lower rank, provided your military strength is sufficient and you’re willing to pay the cost in prestige.
Preparing for a Force Vassalization War
Check De Jure Borders
Forcing vassalage works best when the target is located within your de jure kingdom or empire, as this reduces long-term penalties and improves integration chances. If they’re outside your de jure borders, they’ll be harder to keep loyal.
Build a Strong Army
You need to ensure military superiority before declaring war. This means hiring mercenaries, improving your men-at-arms regiments, and managing alliances. Having more troops and better quality soldiers can make the war quick and decisive.
Accumulate Prestige
The Force Vassalization war costs a high amount of prestige. You must be at least Distinguished in fame level and have several hundred prestige to start the war. Engage in tournaments, feast, or diplomacy missions to increase your prestige before initiating the war.
Declaring War for Vassalage
Using the Right Casus Belli
When viewing a potential target, go to the diplomacy tab and select Declare War. If you’ve unlocked the appropriate perk, and the conditions are met, you’ll see the option to Force Vassalization. Select it and review the war goal before confirming.
War Objectives and Strategy
The objective in a vassalization war is not to conquer territory directly, but to reach 100% war score by defeating the target’s armies, capturing important holdings, and possibly capturing their ruler. Focus on:
- Winning key battles.
- Occupying their capital and other valuable counties.
- Capturing family members or the ruler themselves for quick war score boosts.
Always aim for a quick and clean victory. The longer the war drags on, the more likely it is that other realms will take advantage of your distracted state.
After the War: Managing Your New Vassal
Dealing with Loyalty and Opinion
Once the war is over, your new vassal may not be very happy with you. Their opinion may be negative, and they might consider rebellion if your authority is weak. Consider these actions to improve relations:
- Send a gift to increase opinion.
- Use the Sway scheme to build trust over time.
- Grant them honorary titles or positions on your council.
Also ensure that your crown authority is high enough to discourage rebellion. You may want to increase it before declaring war, so your vassals are more tightly controlled.
Integrating the Vassal
If the target is from a different culture or religion, integration will be more difficult. Consider converting them through religious pressure or cultural reform, especially if they hold powerful duchies. Over time, their lands may become part of your de jure realm, making them easier to manage.
Alternatives to Forced Vassalage
Offer Vassalization Diplomatically
If a neighboring ruler is much weaker than you and shares your culture and religion, you may be able to offer vassalization peacefully. This is always preferable when possible, as it avoids war and its costs. To increase your chances:
- Increase your realm size and power.
- Maintain high diplomacy and good traits.
- Ensure cultural and religious unity.
Subjugation and Holy Wars
Other forms of realm expansion exist, such as subjugation wars (available once per lifetime), or holy wars against realms of different faiths. These offer alternatives if forced vassalage is not viable in your situation.
Tips for Success with Forced Vassalage
- Use forced vassalization on rulers with multiple counties don’t waste it on a single-county count.
- Target neighboring dukes to expand quickly and secure borders.
- Plan several vassalization wars in a row after unlocking the perk to make full use of it before your ruler dies.
- Be prepared for short-term instability after each new vassal joins your realm.
Forcing vassalage in CK3 is one of the smartest and most controlled methods of expanding your realm, especially once you’ve built enough strength and prestige. While the process requires preparation unlocking the right perk, maintaining military dominance, and ensuring diplomatic readiness the rewards are well worth it. By adding powerful rulers as vassals instead of destroying their domains, you retain their local authority while benefiting from their taxes and soldiers. With smart use of forced vassalization, your kingdom or empire can rapidly grow while avoiding the pitfalls of overextension.