A province defects to you, just in peacetime as a result of prolonged rebels. You didn't ask for it, you cannot refuse; it just happens. As a result the newly owned province suffers from high RR due to nationalism for several decades. Example: playing as Oman, Socotra (province of Ethiopia, orthodox religion) defects to me giving about 10-15% RR for many decades, due to nationalism and different religion. What's the point?
I didn't force them to join me; it's their choice. I think such a defect event should give a core for free. Alternative: the province should be free of nationalism without an immediate core. 