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:
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. 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:
Method 2: Demanding Vassalization
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:
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:
