German reunification  German reunification () was the process in 1990 in which the German Democratic Republic (GDR, colloquially East Germany; German: ) became part of the Federal Republic of Germany (FRG, colloquially West Germany; German: ) to form the reunited nation of Germany, as provided by Article 23 of the FRG's then constitution (). The end of the unification process is officially referred to as German unity (), celebrated each year on 3 October as German Unity Day (). Berlin was reunited into a single city, and was once again designated as the capital of united Germany. The East German government started to falter in May 1989, when the removal of Hungary's border fence with Austria opened a hole in the Iron Curtain. It caused an exodus of thousands of East Germans fleeing to West Germany and Austria via Hungary. The Peaceful Revolution, a series of protests by East Germans, led to the GDR's first free elections on 18 March 1990, and to the negotiations between the GDR and FRG that culminated in a Unification Treaty. Other negotiations between the GDR and FRG and the four occupying powers produced the so-called "Two Plus Four Treaty" (Treaty on the Final Settlement with Respect to Germany) granting full sovereignty to a unified German state, whose two parts were previously bound by a number of limitations stemming from their post-World War II status as occupied regions. The 1945 Potsdam Agreement had specified that a full peace treaty concluding World War II, including the exact delimitation of Germany's postwar boundaries, required to be "accepted by the Government of Germany when a government adequate for the purpose is established." The Federal Republic had always maintained that no such government could be said to have been established until East and West Germany had been united within a free democratic state; but in 1990 a range of opinions continued to be maintained over whether a unified West Germany, East Germany, and Berlin could be said to represent "Germany as a whole" for this purpose. The key question was whether a Germany that remained bounded to the east by the Oder–Neisse line could act as a "united Germany" in signing the peace treaty without qualification. Under the "Two Plus Four Treaty" both the Federal Republic and the Democratic Republic committed themselves and their unified continuation to the principle that their joint pre-1990 boundaries constituted the entire territory that could be claimed by a Government of Germany, and hence that there were no further lands outside those boundaries that were parts of Germany as a whole. The post-1990 united Germany is not a successor state, but an enlarged continuation of the former West Germany.