The Nazis believed that in future , the Masurs , as a separate non-German entity , would disappear , while those who would cling to their " foreigness " as one Nazi report mentioned , would be deported . Local Jews were considered by the Nazis to be subhuman and were to be exterminated . The Nazi authorities also executed Polish activists in Masuria and those who remained alive were sent to concentration camps . In August 1943 the Uderzeniowe Bataliony Kadrowe attacked the village of Mittenheide ( Turośl ) in southern Masuria In 1943 " Związek Mazurski " was reactivated secretly by Masurian activists of the Polish Underground State in Warsaw and led by Karol Małłek . Związek Mazurski opposed Nazi Germany and asked Polish authorities during the war to liquidate German property after victory over Nazi Germany to help in agricultural reform and settlement of Masurian population , Masurian iconoclasts opposed to Nazi Germany requested to remove German heritage sites " regardless of their cultural value " . Additionally a Masurian Institute was founded by Masurian activists in Radość near Warsaw in 1943 In the final stages of World War II , Masuria was partially devastated by the retreating German and advancing Soviet armies during the Vistula-Oder Offensive . The region came under Polish rule at the war 's end in the Potsdam Conference . Most of the population fled to Germany or was killed during or after the war , while the rest was subject to a " nationality verification " , organised by the communist government of Poland . As a result , the number of native Masurians remaining in Masuria was initially relatively high , while most of the population was subsequently expelled . Poles from central Poland and the Polish areas annexed by the Soviet Union as well as Ukrainians expelled from southern Poland throughout the Operation Vistula , were resettled in Masuria
Potsdam Conference
Potsdam Conference
Masuria