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 .
Since that time it has been part of Poland .
At the Potsdam Conference , the three Allies assigned the region to Poland administration in August 1945 , and the German - Polish Border Treaty confirmed the annexation in 1990 .
Since that time it has been part of Poland .