If a realm were to attempt to create a colony right inside another realm that they are at war with, out of regions that are clearly too far away from their own capital not to revolt almost immediately, should that be considered a strategic secession? It's not like there's anything else they could do with those regions...
If it's created out of land that they have taken within that same war, I wouldn't call it a strategic secession. Creating puppet states (marches would be a medieval appropriate term) in the wake of your army's passage is a legitimate war tactic.
If it's created out of lands that were held by the parent realm in peace time, then it could be a strategic secession.
