The East Prussian plebiscite, also known as the Allenstein and Marienwerder plebiscite or Warmia, Masuria and Powiśle plebiscite, was a plebiscite for the self-determination of the regions of southern Warmia, Masuria and Powiśle, which had been in parts of the East Prussian Government Region of Allenstein and of the West Prussian Government Region of Marienwerder in accordance with Articles 94 to 97 of the Treaty of Versailles. Wikipedia