While technically Greater Poland was not a German state, the roughly corresponding territory of the Grand Duchy of Posen had been under Prussian control since the First and Second Partition of Poland in the late 18th century.
Kuigi tehniliselt ei olnud Suur-Poola Saksa riik, oli laias laastus vastav Poseni suurhertsogkonna territoorium Esimesest ja Teisest Poola jagamisest saati 18. sajandi lõpul Preisi kontrolli all.