The Marienwerder Region was dissolved in 1945 following Nazi Germany 's defeat in the war . The Soviet conquerors handed the region 's territory to Poland in March 1945 . Since that time it has been part of Poland . At the Potsdam Conference , the three Allies assigned the region to Polish administration in August 1945 , and the German-Polish Border Treaty confirmed the annexation in 1990
Potsdam Conference
Potsdam Conference
Marienwerder (region)