Removal of Hungary's border fence with Austria in the context of "Revolutions of 1989"

German reunification (German: Deutsche Wiedervereinigung), also known as the expansion of the Federal Republic of Germany (BRD), was the process of re-establishing Germany as a single sovereign state, which began on 9 November 1989 and culminated on 3 October 1990 with the dissolution of the German Democratic Republic and the integration of its re-established constituent federated states into the Federal Republic of Germany to form present-day Germany. This date was chosen as the customary German Unity Day, and has thereafter been celebrated each year as a national holiday. On the same date, East and West Berlin were also reunified into a single city, which eventually became the capital of Germany.

The East German government, controlled by the Socialist Unity Party of Germany (SED), started to falter on 2 May 1989, when the removal of Hungary's border fence with Austria opened a hole in the Iron Curtain. The border was still closely guarded, but the Pan-European Picnic and the indecisive reaction of the rulers of the Eastern Bloc started off an irreversible movement. It allowed an exodus of thousands of East Germans fleeing to West Germany via Hungary. The Peaceful Revolution, part of the international revolutions of 1989 including a series of protests by East German citizens, led to the fall of the Berlin Wall on 9 November 1989 and the GDR's first free elections on 18 March 1990, and then to negotiations between the two countries that culminated in a Unification Treaty. Other negotiations between the two Germanies and the four occupying powers in Germany produced the Treaty on the Final Settlement with Respect to Germany, which granted on 15 March 1991 full sovereignty to a reunified German state, whose two parts had previously been bound by a number of limitations stemming from their post-World War II status as occupation zones, though it was not until 31 August 1994 that the last Russian occupation troops left Germany.

The Revolutions of 1989, also known as the Fall of Communism, were a wave of liberal democratic movements that resulted in the collapse of most Marxist–Leninist governments in the Eastern Bloc and other parts of the world (this wave is sometimes referred to as the "Autumn of Nations", in reference to the Revolutions of 1848 as the "Spring of Nations"). The revolutions of 1989 were a key factor in the dissolution of the Soviet Union—one of the two superpowers—and abandonment of communist regimes in many parts of the world, some of which were violently overthrown. These events drastically altered the world's balance of power, marking the end of the Cold War and beginning of the post-Cold War era.

The earliest recorded protests, which led to the revolutions, began in Poland on 14 August 1980, the massive general strike which led to the August Agreements and establishment of Solidarity, the first and only independent trade union in the Eastern Bloc, whose peak membership reached 10 million. The main region of the 1989 revolutions was Central Europe, starting in Poland with the 1988 Polish strikes, and continued in Hungary, East Germany, Bulgaria, Czechoslovakia, and Romania. On 4 June 1989, Poland conducted the first elections that led to the dissolution of the communist government, with Solidarity winning an overwhelming victory, leading to the peaceful fall of communism in Poland. Influenced by Poland, Hungary organised round table-format talks and began dismantling its section of the Iron Curtain. In August 1989, over a quarter of the Baltic states population physically chained for 675 kilometres (419 mi) in the Baltic Way protesting the occupation by the Soviet Union, while the opening of a border gate between Austria and Hungary set in motion a peaceful chain reaction, in which the Eastern Bloc disintegrated. This led to mass demonstrations in cities of East Germany and the fall of the Berlin Wall in November 1989, which served as the symbolic gateway to German reunification in 1990. A feature common to these developments was the extensive use of campaigns of civil resistance, demonstrating popular opposition to the continuation of one-party rule and contributing to pressure for change. Romania was the only country in which citizens and opposition forces used violence to overthrow its communist regime, although Romania was politically isolated from the rest of the Eastern Bloc.