At the Yalta Conference and Potsdam Conference of 1945 , the victorious Allies , at Stalin 's demand , divided East Prussia into the two parts now known as Oblast Kaliningrad ( in Russia ) and the Warmian-Masurian Voivodeship ( in Poland ) , making Warmia part of Poland again . Most of the population was evacuated or fled the advancing Red Army in 1945 . Prior to the Potsdam Conference , during the Soviet winter 1945 offensive ( Vistula – Oder Offensive ) , the Red Army overran Warmia
Potsdam Conference
Potsdam Conference
Warmia