Theres a clear difference between posession and demonisation. Posession has something to do with ownership and theres 2 cases of that.
1. a person looses control of himself like the man with legion who wasnt himself anymore but completely are taken over
2. Unsaved people are owned which also oppression in ways
Demonisation is when people are saved but are influenced still by demons/evil spirits/unclean spirits in some area of life which can sometimes seem like posession depending on how much power they have over that specific area.
there ya got a short version of it