Following the outbreak of World War II in September 1939, the Soviets annexed a massive portion of the eastern part of Poland (November 1939) in the wake of an August 1939 agreement between the Reich and the USSR. After the Nazis' defeat in 1945, Poland did not regain its Soviet-annexed territory; instead, Polish communists, directed by the Soviets, expelled the remaining Germans (those who had not been evacuated or fled before) from the areas of Lower Silesia, Upper Silesia, Pommerania, East Brandenburg, and East Prussia and replaced them with Poles, most of whom were expelled from Soviet-occupied areas that had previously formed part of Poland. About half of East Prussia became the newly created Soviet territory of Kaliningrad Oblast (officially established in 1946), where Soviet citizens replaced the former German residents. The Potsdam Agreement of August 1945 specified or endorsed the shifting of borders.