Irredentism – (Italian: irredentismo)[1] is one state’s desire to annex the territory of another state.
I’m surprised I haven’t seen this term used in the context of the Ukraine war by Russia. I found in at the end of chapter 14 of V. by Pynchon:
“Rumor had it that a week or so later the lady V. ran off with one Sgherraccio, a mad irredentist.”