How To Vassalize a Nation in EU4

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There are three ways to vassalize nations:

  1. Offering it diplomatically to willing nations
  2. Demanding it in war
  3. Completely conquering a nation and then releasing them

Method 1: Offering Vassalization

Independent nations can be vassalized diplomatically if:

  • They have less than 100 development
  • They’re allied with you
  • They have at least 190 opinion of you
  • They must be at peace
  • You don’t own any of their core provinces

Most importantly, they must be willing to become your vassals.

The best way to check this is by using the Production Interface:

Bregenz Is Willing to Become an Austrian Vassal / EU4
Bregenz Is Willing to Become an Austrian Vassal
  1. Open the Production Interface (hotkey: b)
  2. Go to the Diplomacy tab (hotkey: 0)
  3. Switch to the Influence actions sub-tab (hotkey: d)
  4. Select the “Offer Vassalization” action
  5. Choose a nation to vassalize

Vassalization Acceptance

Before you woo a nation and start improving your relations, you should first check if they’ll accept your offer.

In the Production Interface, you’ll see a list of nations and how likely they are to become your vassals.

Hover over each of them to check what’s stopping them from becoming your vassal.

Increasing the Positive Modifiers Here Can Make Mulhouse a Potential Vassal / EU4
Increasing the Positive Modifiers Here Can Make Mulhouse a Potential Vassal

To get them to become willing prospects, all you need to do is add more positive modifiers and remove the negative ones.

Here’s a list of things that can affect vassalization acceptance:

Cause Modifier
Target’s attitude toward you +10 for Ally, Friendly, or Threatened
-20 for Neutral
-100 for Hostile or Outraged
How much they Trust you +1 to +10 with 55 to 100 trust
0 at 50 trust
-10 to -40 with 45 to 30 trust
-2000 with less than 30 trust
Your diplomatic reputation +3 per positive reputation
-3 per negative reputation
“Winter Palace”
Great Project in St. Petersburg
+15 to +30
Your economy size relative to your target +30 to -90
Your military power relative to your target +20 to -40
The difference between your government ranks +10 per rank higher than them
-30 per rank lower than them
Target’s government rank -10 for kingdoms
-20 for empires
Target is a member of the HRE -25 if you’re also a member
-75 if you’re not a member
Target is a merchant republic -30
You’re not in the same religious group -20
You have a different religion but is still in the same religion group -10
The distance between your borders -0.5 per distance

Method 2: Demanding Vassalization

Austria Demands Munich to Bend the Knee / EU4
Austria Demands Munich to Bend the Knee

In wars where you’re allowed to take provinces, you also have the option to force an enemy to become your vassal.

This peace term becomes available when you’ve occupied an enemy’s capital. Allies of the enemy war leader can also be vassalized this way.

Nations vassalized in war will have a -200 opinion modifier against you. This decays by 1% per month.

The costs for doing this depends on the loser’s development.

  • 1% War Score per 2 Dev
  • 0.5 Diplo Mana per 1 Dev
  • 0.5 Aggressive Expansion per 1 Dev

Since wars are limited to 100% war score, you can only vassalize a nation with no more than 200 development.

However, you can negate the mana cost as well as reduce the AE impact and war score cost with these specific CBs:

Casus Belli Impact of Development on Aggressive Expansion War Score Cost Reduction Availability
Subjugation 100% 100% Granted by missions and Noble estate agendas
Excommunicated Ruler 50% 100% For neighbors of an excommunicated nation
Tribal Conquest/Feud 75% 100% For steppe nomads and tribes
Spread/Crush the Revolution 50% 50% Available during the Age of Revolutions
Religious League 50% 50% Unique war during the Age of Reformation
Flower Wars 50% 100% For nations with the Nahuatl state religion
The Nobles Estate Occasionally Has an Agenda to Subjugate a Specific Nation / EU4
The Nobles Estate Occasionally Has an Agenda to Subjugate a Specific Nation

Method 3: Releasing a Conquered Country as a Vassal

When a nation only has a few provinces left, it’s better to fully conquer them and then release them as a vassal. This lets you bypass the negative opinion modifier.

Here’s how to do it:

  1. Right-click on your own provinces to open your Diplomacy view
  2. Press the “Create Subject” button in the lower-right
  3. Scroll all the way down to find your recently conquered foe
“Create Subject” Button in the Diplomacy View / EU4
“Create Subject” Button in the Diplomacy View
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Louie Nelson Zafico

As a frustrated otter who dreams of getting published, Louie instead wastes his life cuddling his cats. He spent his childhood playing Suikoden, grew up with Total War, and matured (somewhat) with EU4. He hopes to someday find a geopolitical JRPG with the 4X systems of a Paradox game.