The ethnic displacement of Poles ( and also of ethnic Germans , covered in a separate article ) was agreed to by the Allied leaders : Winston Churchill of the United Kingdom , Franklin D. Roosevelt of the U.S. , and Joseph Stalin of the USSR , during the conferences at both Tehran and Yalta . The Polish transfers were among the largest of several post-war expulsions in Central and Eastern Europe , which displaced a total of about twenty million people
Yalta
Yalta Conference
Polish population transfers (1944–1946)