In 1990, the former Soviet-bloc countries began to hold free elections. The general trend, which went in fits and starts in some places, was to definitively oust the Communist parties. However, remnants of those parties were voted into power in some places, later on, in the form of center-left social democratic parties.
I recall being skeptical at the time, as future election dates were announced in those countries. Knowing that the outgoing regimes could be trusted about as far as one could throw a hammer and sickle, I was suspicious that the Communists would try to finagle their way out of those commitments. But, for the most part, the game was well and truly over, and they realized that there was nothing for them to do but step aside.
East Germany had a different situation than the others did. In all of the Soviet-bloc countries, there was no longer a raison d’être for the Marxist-Leninist regimes. But that had an additional implication in East Germany, where there was therefore no longer a raison d’être for it as a separate state.
As World War II was ending, the allies carved Germany up into four occupation zones, one each for the U.S., the Soviet Union, Britain and France. The plan was to reunite Germany as soon as order could be reestablished, and free elections set up.
That plan fell apart as soon as Harry Truman realized that the trust that his predecessor's administration had placed in Joseph Stalin was naive. The Cold War began, and the wartime allies were cooperating as little as possible, regarding Germany.
By 1949, no longer willing to wait for a reunification agreement, the Soviet Union set up the German Democratic Republic in East Germany, and the others established the German Federal Republic in West Germany. At that time, it was unclear when, if ever, Germany would be unified.
Fast forward to the late 1980s, and that distant goal started to seem imminent. When Soviet leader Mikhail Gorbachev toured West Germany, he received a tumultuous welcome. The Economist noted at the time that Gorbymania had turned into Gorbasm. That was largely based on the view (which turned out to be correct) that he wouldn't move to prevent German reunification.
Not all Europeans were so ecstatic, however.
Western European leaders, including Margaret Thatcher, were wary of the consequences of changing the existing European order.
When the Soviet Union expressed security concerns about Germany, which had caused huge suffering when it attacked the USSR in 1941, the Economist dismissed those fears, pointing out that the only time a German army had invaded another country post-1945, was in 1968, when the East German army participated in the Warsaw Pact invasion of Czechoslovakia.
Although Gorbachev knew that his country could not continue to dominate any part of Germany, his hope was probably that a neutral East Germany could be maintained as a buffer against the eastward expansion of NATO. That remains a concern for post-Soviet Russia, and was a factor in its war with Georgia in 2008.
Chancellor Helmut Kohl of the Federal Republic of Germany overcame such opposition by strongly pushing for reunification. His victory was probably largely based on the fact that the further economic deterioration of East Germany left the world with no other choice. The form of the unification was not a merger, but rather a matter of the East German Laender joining the Federal Republic. The eastern Laender fell like rotten apples into the Bonn basket.
As a result of all that, the East Germans voted twice in 1990. March 18 saw the only democratic election in the history of the German Democratic Republic. They elected a parliament whose main task was to prepare the east for unification. That event, for which the principals had originally penciled in a later date, was moved up to October 3, in light of the increasingly precarious state of the eastern economy.
The democratic all-German election that was supposed to take place after a brief postwar interim, finally happened on December 2, 1990, a mere 45 years late. The coalition government that was led by Kohl's Christian Democrats was reelected, with strong support in both east and west.