The territorial changes of Poland immediately after World War II were very extensive, the Oder–Neisse line[1] became Poland's western border and the Curzon Line[2] its eastern border. In 1945, after the defeat of Nazi Germany, Poland's borders were redrawn in accordance with the decisions made first by the Allies at the Tehran Conference of 1943 where the Soviet Union demanded the recognition of the military outcome of the top secret Nazi–Soviet Pact of 1939[3] of which the West was unaware.
The same Soviet stance was repeated by Joseph Stalin again at the Yalta Conference with Roosevelt and Churchill in February 1945, but a lot more forcefully in the face of the looming German defeat.[4] The new borders were ratified at the Potsdam Conference of August 1945 exactly as proposed by Stalin who already controlled the whole of East-Central Europe.[4] Harry Truman remembered:
I remember at Potsdam, we got to discussing a matter in eastern Poland, and it was remarked by the Prime Minister of Great Britain that the Pope would not be happy over the arrangement of that Catholic end of Poland. And the Generalissimo, the Prime Minister of Russia leaned on the table, and he pulled his mustache like that, and looked over to Mr. Churchill and said: Mr. Churchill, Mr. Prime Minister, how many divisions did you say the Pope had?[5]
Poland lost large territories to the Soviet Union (today those areas are located in Lithuania, Belarus and Ukraine). Poland was instead given the Free State of Danzig and the German areas east of the rivers Oder and Neisse. The ethnic cleansing of both Polish and Germans 1945-46 included many millions of people.[6][7] The Polish territory 1919-1939 covered an area of 386,418 square kilometres (149,197 square miles).[8] But from 1947, Poland's territory was reduced to 312,679 square kilometres (120,726 square miles), so the country lost 73,739 square kilometres (28,471 square miles) of land. This difference amounts almost to the size of the Czech Republic, although Poland ended up with a much longer coastline on the Baltic Sea compared to its 1939 borders.
