Where is the aggressive expansion of your country listed? And how much can be "tolerated" before one is in danger of a coalition war? I guess I never looked in the right place.
If you take provinces in a peace treaty, gaining AE, and then immediately release the conquered territory as a vassal will that reduce the AE? Or do you need to simply force the warred nation to release the nation during the peace deal to avoid the AE and then diplo-vassalize?
Two years, now.
Completely gone in 2 years? I did not know this.
That's worth the wait if it causes the coalition to break apart.
Where is the aggressive expansion of your country listed?
If you have positive relations and they are small you can ally them (which automatically forces them out of the coalition) and then cancel the alliance right before attacking them.
I usually do it against OMP's that I couldnt otherwise annex.
No
The minimum time for an AI nation to be in a coalition is two years (down from five.) After joining a coalition, they cannot leave it until two years have passed, regardless of their attitude and opinion of the nation.
It does not mean they always leave after two years. They leave when the AI coding allows them to, which factors in their Attitude (Outraged, Hostile, Threatened, Friendly, etc), their current numerical opinion of you, and how much AE you have. Possibly also other factors, like the AI leader's personality and whether they Want to Conquer you - though those things also feed directly into their Attitude, so they may not be direct contributors to Coalition decisions as well.
To summarise, an AI nation will leave a coalition when both of the following are true:
- they have been in it for 24 or more months;
- their current stance towards the coalition target means that they no longer want a coalition against them