I have to write a long History essay about territories which were once occupied by one people, but no longer are. Is there a term for that, something like once-[insertpeoplehere]-occupied?
If the fact that the country was at the time occupied is important, such as wartime, use then-occupied
He was sent to then-occupied France to serve in a battalion of former Soviet prisoners of war...
By April of 1945, eight months following Nazi massacres in the Saulx valley of then-occupied France,
If the country was occupied as a colony or dominion, then use French Senegal, British India, etc., again if the fact of occupation is relevant to the issue.