The Oder Neisse line marks the post-1945 border between Poland and Germany. It runs from the northernmost point of the Czech Republic to the Baltic Sea at the Oder estuary. The border follows primarily the River Oder/ Odra and Lusatian Neisse river.
The Oder-Neisse Line was determined at the Yalta Conference in February 1944 and finalised at the Potsdam conference in August 1945. President Roosevelt signed the Yalta Agreement for the government of the United States, Prime Minister Churchill for England, the Chairman of the Ministerial Council Stalin for the USSR. Truman signed the Potsdam Agreement for the USA, Attlee for England, Stalin for the Soviet Union. The French government added its official approval later. According to the Yalta and Potsdam Declarations, the Oder-Neisse Line was drawn to make a future German attack less likely and to give the Polish people a secure western border. It was also, at 472 km long, the shortest possible border based on rivers between Poland and Germany.
This new Oder-Neisse border removed vast areas from what had been Germany prior to the Second World War. Most of Silesia, more than half of Pomerania, the eastern portion of Brandenburg, part of Saxony, and most of East Prussia (Masuria and Warmia) were after 1945 no longer part of Germany but part of Poland, while the former German territory of north east of East Prussia was directly annexed by the Soviet Union.
Although, Poland gained territory in the west with the creation of the Oder-Neisse border it lost an even larger area in the east. This area known as Kresy (or Eastern borderlands), prior to the Second World War part of Poland, today lies in western Ukraine, western Belarus, and eastern Lithuania. The subject of the lost Polish lands in the east will be covered in more detail in future posts but for the moment take a look at the moving map at the top of this page to get an idea of the scale of these post-war border changes.