Reunification of Germany
On 28 November 1989—two weeks after the fall of the Berlin Wall—West German Chancellor Helmut Kohl announced a 10-point program calling for the two Germanies to expand their cooperation with the view toward eventual reunification.
Initially, no timetable was proposed. However, events rapidly came to a head in early 1990. First, in March, the Party of Democratic Socialism—the former Socialist Unity Party of Germany—was heavily defeated in East Germany's first free elections. A grand coalition was formed under Lothar de Maizière, leader of the East German wing of Kohl's Christian Democratic Union, on a platform of speedy reunification. Second, East Germany's economy and infrastructure underwent a swift and near-total collapse. While East Germany had long been reckoned as having the most robust economy in the Soviet bloc, the removal of Communist discipline revealed the ramshackle foundations of that system. The East German mark had been practically worthless outside of East Germany for some time before the events of 1989–90, further magnifying the problem.
Discussions immediately began for an emergency merger of the Germanies' economies. On 18 May 1990, the two German states signed a treaty agreeing on monetary, economic and social union. This came into force on 1 July 1990, with the Deutsche Mark replacing the East German mark as the official currency of East Germany. The Deutsche Mark had a very high reputation among the East Germans and was considered stable. While the GDR transferred its financial policy sovereignty to West Germany, the West started granting subsidies for the GDR budget and social security system. At the same time many West German laws came into force in the GDR. This created a suitable framework for a political union by diminishing the huge gap between the two existing political, social, and economic systems.
A reunification treaty between West Germany and the GDR was negotiated in mid-1990, signed on 31 August of that year and finally approved by large majorities in the legislative chambers of both countries on 20 September 1990. The amendments to the Federal Republic's Basic Law that were foreseen in the Unification Treaty or necessary for its implementation were adopted by the Federal Statute of 23 September 1990. After that last step Germany was officially united at 00:00 CET on 3 October 1990. East Germany joined the Federal Republic as the five states of Brandenburg, Mecklenburg-Vorpommern, Saxony, Saxony-Anhalt and Thuringia. These states had been the five original states of East Germany, but had been abolished in 1952 in favour of a centralised system. As part of the 18 May treaty, the five East German states had been reconstituted on 23 August. At the same time, East and West Berlin reunited into one city, which became a city-state along the lines of the existing city-states of Bremen and Hamburg.
The process chosen was one of two options implemented in the West German constitution (Basic Law) of 1949. Via that document's (then-existing) Article 23, any new Länder (German federative states), could adhere to the Basic Law by a simple majority vote. Thus the states' parliaments would vote in for their adhesion. The initial eleven joining states of 1949 comprised the Trizone and West Berlin. However the latter was legally inhibited by Allied objection due to the status of the city as a quadripartite allied occupation area. In 1957 the Saar Protectorate joined West Germany under the Article 23 procedure as Saarland. As the five refounded eastern German states formally joined the Federal Republic using the Article 23 procedure, the area in which the Basic Law was in force simply extended to include them. The alternative would have been for East Germany to join as a whole along the lines of a formal union between two German states that then would have had to, amongst other things, create a new constitution for the newly established country.
Under the model that was chosen, however, the territory of the former German Democratic Republic was simply incorporated into the Federal Republic of Germany, and accordingly the Federal Republic of Germany, now enlarged to include the Eastern States, continued legally to exist under the same legal personality that was founded in May 1949.
Thus, the reunification was not a merger that created a third state out of the two, but an incorporation, by which West Germany absorbed East Germany. Thus, on Unification Day, 3 October 1990, the German Democratic Republic ceased to exist, giving way to five new Federal States, and East and West Berlin were also unified as a single city-state, forming a sixth new Federal State. The new Federal States immediately became parts of the Federal Republic of Germany, so that it was enlarged to include the whole territory of the former East Germany and Berlin.
The practical result of that model is that the now expanded Federal Republic of Germany continued to be a party to all the treaties it had signed prior to the moment of reunification, and thus continued the same membership of the U.N., NATO, the European Communities, etc.; also, the same Basic Law and the same laws that were in force in the Federal Republic continued automatically in force, but now applied to the expanded territory.
To facilitate this process and to reassure other countries, some changes were made to the "Basic Law" (constitution). Article 146 was amended so that Article 23 of the current constitution could be used for reunification. After the five "New Länder" of East Germany had joined, the constitution was amended again to indicate that all parts of Germany are now unified. Article 23 was rewritten and it can still be understood as an invitation to others (e.g. Austria) to join, although the main idea of the change was to calm fears in (for example) Poland, that Germany would later try to rejoin with former eastern territories of Germany that were now Polish or parts of other countries in the East. The changes effectively formalised the Oder-Neisse line as Germany's permanent eastern border. These amendments to the Basic Law were mandated by Article I, section 4 of the Two Plus Four Treaty.
While the Basic Law was modified rather than replaced by a constitution as such, it still permits the adoption of a formal constitution by the German people at some time in the future.
To commemorate the day that marks the official unification of the former East and West Germany in 1990, 3 October has since then been the official German national holiday, the Day of German Unity (Tag der deutschen Einheit). It replaced the previous national holiday held in West Germany on 17 June commemorating the Uprising of 1953 in East Germany and the national holiday on 7 October in the GDR.