The entirety of Germany was occupied and administered by the Allies of World War II, from the Berlin Declaration on 5 June 1945 to the establishment of West Germany on 23 May 1949. Nazi Germany was stripped of its sovereignty and its government was entirely dissolved. After Germany formally surrendered on Tuesday, 8 May 1945, the four countries representing the Allies (the United States, United Kingdom, Soviet Union, and France) asserted joint authority and sovereignty through the Allied Control Council (ACC).
Germany after the war was a devastated country – roughly 80 percent of its infrastructure was in need of repair or reconstruction – which helped the idea that Germany was entering a new phase of history ("zero hour"). At first, Allied-occupied Germany was defined as all territories of Germany before the 1938 Nazi annexation of Austria. The Potsdam Agreement on 2 August 1945 defined the new eastern German border by giving Poland and the Soviet Union all regions of Germany east of the Oder–Neisse line (eastern parts of Pomerania, Neumark, Posen-West Prussia, East-Prussia and most of Silesia) and divided the remaining "Germany as a whole" into four occupation zones, each administered by one of the Allies.
All territories annexed by Germany before the war from Austria and Czechoslovakia were returned to these countries. The Memel Territory, annexed by Germany from Lithuania before the war, was annexed by the Soviet Union in 1945 and transferred to the Lithuanian Soviet Socialist Republic. All territories annexed by Germany during the war from Belgium, France, Italy, Luxembourg, Poland, the Soviet Union and Yugoslavia were returned to their respective countries. Deviating from the occupation zones planned according to the London Protocol in 1944, at Potsdam, the United States, United Kingdom and the Soviet Union approved the detachment from Germany of the territories east of the Oder–Neisse line, with the exact line of the boundary to be determined in a final German peace treaty. This treaty was expected to confirm the shifting westward of Poland's borders, as the United Kingdom and United States committed themselves to support the permanent incorporation of eastern Germany 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 Agreement 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 U.S. forces at the end of hostilities, mostly lying eastward of the July 1945-established inner German border, was temporary. After two months during which they 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 which persuaded the Soviet Union to allow American, British and French forces into their designated sectors in Berlin, which occurred at roughly the same time; the need for intelligence gathering (Operation Paperclip) may also have been a factor. After the Soviet withdrawal from the Allied Control Council on 20 March 1948, the split had led to the 1949 establishment of two new German states, the Federal Republic of Germany (FRG, West Germany) and the German Democratic Republic (GDR, East Germany).
The American zone in Southern Germany consisted of Bavaria (without the Rhine Palatinate Region and the Lindau District, both part of the French zone) and Hesse (without Rhenish Hesse and Montabaur Region, both part of the French zone) with a new capital in Wiesbaden, and of northern parts of Württemberg and Baden. Those formed Württemberg-Baden and became northern portions of the present-day German state of Baden-Württemberg founded in 1952.
The ports of Bremen (on the lower Weser River) and Bremerhaven (at the Weser estuary of the North Sea) were also placed under U.S. control because of the U.S. request to have certain toeholds in Northern Germany.
The headquarters of the American military government was the former IG Farben Building in Frankfurt am Main.
By May 1945 the British and Canadian Armies had liberated the Netherlands and had conquered Northern Germany. The Canadian forces went home following the German surrender, leaving Northern Germany to be occupied by the British.
The British Army of the Rhine was formed on 25 August 1945 from the British Liberation Army.
In July the British withdrew from Mecklenburg's capital Schwerin which they had taken over from the Americans a few weeks before, as it had previously been agreed to be occupied by the Soviet Army. The Control Commission for Germany (British Element) (CCG/BE) ceded more slices of its area of occupation to the Soviet Union – specifically the Amt Neuhaus of Hanover and some exclaves and fringes of Brunswick, for example the County of Blankenburg, and exchanged some villages between British Holstein and Soviet Mecklenburg under the Barber-Lyashchenko Agreement.
Within the British zone of occupation, the CCG/BE re-established the city of Hamburg as a German state, but with borders that had been drawn by the Nazi government in 1937. The British also created the new German states of:
Schleswig-Holstein – emerging in 1946 from the Prussian Province of Schleswig-Holstein;
Lower Saxony – the merger of Brunswick, Oldenburg, and Schaumburg-Lippe with the state of Hanover in 1946; and
North Rhine-Westphalia – the merger of Lippe with the Prussian provinces of the Rhineland (northern part) and Westphalia – during 1946–47.
Also in 1947, the American zone of occupation being inland had no port facilities – thus the Free Hanseatic City of Bremen and Bremerhaven became exclaves within the British zone.
The British headquarters were originally based in Bad Oeynhausen from 1946, but in 1954 it was moved to Mönchengladbach where it was known as JHQ Rheindahlen.
Another special feature of the British zone was the enclave of Bonn. It was created in July 1949 and was not under British or any other allied control. Instead it was under the control of the Allied High Commission. In June 1950, Ivone Kirkpatrick became the British High Commissioner for Germany. Kirkpatrick carried immense responsibility particularly with respect to the negotiation of the Bonn–Paris conventions during 1951–1952, which terminated the occupation and prepared the way for the rearmament of West Germany.
Belgian, Polish and Norwegian zones