I'm expanding moderately quickly on mainland Europe, sometimes peacefully and sometimes not, and large neighbouring nations are not too happy with this, even though we don't share particularly long borders. Unlike other modifiers, there doesn't seem to be an obvious way to remove this penalty in relations, sometimes going all the way to -200.
Is this somehow related to the number of claims and cores they have in my provinces, or vice versa? Is there a formula for calculating border friction, and what can I do to reduce it?
Best Answer
As of Patch 1.2.1, border friction is entirely dependent on the base tax of the bordering provinces from both nations. The relations penalty is 1 point per base tax.
Source: Paradox Forums