Ok for everyone new to eu5, whenever you win a war against someone say little Timmy, There is a button you may be able to press to make him a vassal
NEVER, under any circumstance, hit this button
The second little Timmy gets vassaled he’ll start plotting your demise, you see he can ask every country in Europe to head his plea, and they will all by sympathetic to his cause. Even France and England will set aside their differences in the 100 years war to fight against the oppressor, in unison, that took over little Timmy’s sand castle and is making him pay a penny a month in exchange for “protection”
When this happens they will also universally agree to hate little Timmy’s oppressor essentially forever with negative opinion modifiers, making your aggressive expansion skyrocket. Where as before taking a map from the local library may be deemed a slap on the wrist, it will now be justification to have you be hanged at The Hague for your crimes against humanity
Please paradox stop having every man woman and child fight to the death to liberate little Timmy