Post-Nazi German occupation borders and territories from 1945 to 1949. British (green), French (blue), American (orange) and Soviet (red) occupation zones. Saar Protectorate (light blue) in the west under the control of France. Berlin is the quadripartite area shown within the red Soviet zone. Bremen consists of the two orange American exclaves in the British sector.
At Potsdam, the United States, United Kingdom and the Soviet Union approved the detachment from 'Germany as a whole' of the German eastern territories east of the Oder–Neisse line; with the exact line of the boundary to be determined at a final German Peace Treaty. This treaty was expected to confirm the "shifting westward" of Poland's borders, as the United Kingdom and the United States committed themselves to support in any future peace treaty the permanent incorporation of former eastern German territories into Poland and the Soviet Union. From March 1945 to July 1945, these former eastern territories of Germany had been administered under Soviet military occupation authorities, but following the Potsdam Conference they were handed over to Soviet and Polish civilian administrations and ceased to constitute part of Allied-occupied Germany.
In the closing weeks of fighting in Europe, United States forces had pushed beyond the agreed boundaries for the future zones of occupation, in some places by as much as 320 km (200 miles). The so-called line of contact between Soviet and American forces at the end of hostilities, mostly lying eastward of the July 1945-established inner German border, was temporary. After two months in which they had held areas that had been assigned to the Soviet zone, U.S. forces withdrew in the first days of July 1945. Some have concluded that this was a crucial move that persuaded the Soviet Union to allow American, British and French forces into their designated sectors in Berlin, which occurred at roughly the same time (July 1945), although the need for intelligence gathering (see Operation Paperclip) may also have been a factor.