Before June 1 , 1945 , some 400,000 Germans managed to cross the Oder and Neisse rivers eastward before Polish authorities closed the river crossings , another 800,000 entered Silesia from Czechoslovakia , bringing up Silesia 's population to 50 % of the pre-war level . This led to the odd situation of treks of Germans moving about in all directions , to the east as well as to the west , each warning the others of what would await them at their destination After the Potsdam Conference , Poland was officially in charge of the territories east of the Oder – Neisse line . Despite the fact that article 8 of Potsdam agreement from August 2 , 1945 stated that " population transfer " should be performed in ordered and humane manner , and should not commence until after the creation of an expulsion plan approved by the Allied Control Council , the expulsions continued without rules and were associated with many criminal acts
Potsdam Conference
Potsdam Conference
Flight and expulsion of Germans from Poland during and after World War II