The replacement of Masurian in favor of German was not completed by the time the Soviet Red Army conquered Masurian East Prussia in January 1945 , in World War II . The territory was transferred to Poland according to the postwar Potsdam Conference . During the wartime fighting and post-war deportations in the subsequent decades , most Masurian-speakers left Masuria for western Germany , especially to post-war West Germany , where they were quickly assimilated into the German mainstream
Potsdam Conference
Potsdam Conference
Masurian dialect