I have found in my one campaign that do to the AI's anti expansionism mindset once you start taking a little and the wars just start rolling in.

I never really have a desire for expanding as greatly as I do, but in the end it is just to tempting to wipe out a faction rather then just have them build on your door step for years, and years, and years.
When I took half of Pol-Lith, I was more then content to just let them be till the end of time as a Russian buffer. Once they started moving 2000-3000 troops along my border though, it was time to deal with it.

Russia became my enemy when they invaded and burned much of my city.

Venice I took do to the fact they took out my fleet.

Saxony and Wutemburg do to refusal to become Protectorates, same with Hanover. Which later leads others to become my protectorates.


The only groups I fight without much reason other then land were the Ottomans (but my prince starts off with a hate ottoman trait so with in reason as Austria)

and the Natives of America