Third cabinet, 1987–1991
After the 1987 federal elections, Kohl won a slightly reduced majority and formed his third cabinet. The SPD's candidate for chancellor was the Minister-President of North Rhine-Westphalia, Johannes Rau.
In 1987, Kohl hosted East German leader Erich Honecker – the first ever visit by an East German head of state to West Germany. This is generally seen as a sign that Kohl pursued Ostpolitik, a policy of détente between East and West that had been begun by the SPD-led governments (and strongly opposed by Kohl's own CDU) during the 1970s.
The CDU's general secretary, Heiner Geißler, considered the party to be in a downward spiral following the relatively poor showing in the 1987 elections. Behind the scenes, he attempted to find a majority to unseat Kohl as the party's chairman and replace him with Lothar Späth, the Minister-president of Baden-Württemberg. Before the CDU party convention in Bremen started on 11 September 1989, Kohl was diagnosed with an inflammation of his prostate. His doctor recommended immediate surgery, but Kohl refused to miss the convention and attended while wearing a catheter and with his doctor by his side, whom he introduced as his new speech writer. In the end, the "coup" was unsuccessful, as Kohl was re-elected as chairman with 79.52% of the votes. Späth, who did not stand for the position of chairman after support for Kohl became apparent, was punished by his party, failing to be elected as vice-chairman with just 357 of 731 votes. Geißler meanwhile was relieved of his duties as general secretary and replaced by Volker Rühe.
Following the breach of the Berlin Wall and the collapse of the East German Communist regime in 1989, Kohl's handling of the East German issue would become the turning point of his chancellorship. Kohl, like most West Germans, was initially caught unaware when the Socialist Unity Party was toppled in late 1989. Well aware of his constitutional mandate to seek German unity, he immediately moved to make it a reality. Taking advantage of the historic political changes occurring in East Germany, Kohl presented a ten-point plan for "Overcoming the division of Germany and Europe" without consulting his coalition partner, the FDP, or the Western Allies. In February 1990, he visited the Soviet Union seeking a guarantee from Mikhail Gorbachev that the USSR would allow German reunification to proceed. One month later, the Party of Democratic Socialism – the renamed SED – was roundly defeated by a grand coalition headed by the East German counterpart of Kohl's CDU, which ran on a platform of speedy reunification.
On 18 May 1990, Kohl signed an economic and social union treaty with East Germany. This treaty stipulated that when reunification took place, it would be under the quicker provisions of Article 23 of the Basic Law. That article stated that any new states could adhere to the Basic Law by a simple majority vote. The alternative would have been the more protracted route of drafting a completely new constitution for the newly reunified country, as provided by Article 146 of the Basic Law. However, the Article 146 process would have opened up contentious issues in West Germany. Even without this to consider, by this time, East Germany was in a state of utter collapse. In contrast, an Article 23 reunification could be completed in as little as six months.
Over the objections of Bundesbank president Karl Otto Pöhl, he allowed a 1:1 exchange rate for wages, interest and rent between the West and East Marks. In the end, this policy would seriously hurt companies in the new federal states. Together with Foreign Minister Hans-Dietrich Genscher, Kohl was able to resolve talks with the former Allies of World War II to allow German reunification. He received assurances from Gorbachev that a reunified Germany would be able to choose which international alliance it wanted to join, although Kohl made no secret that he wanted the reunified Germany to inherit West Germany's seats at NATO and the EC.
A reunification treaty was signed on 31 August 1990 and was overwhelmingly approved by both parliaments on 20 September 1990. At midnight Central European Time on 3 October 1990, East Germany officially ceased to exist, and its territory joined the Federal Republic as the five states of Brandenburg, Mecklenburg-Vorpommern, Saxony, Saxony-Anhalt and Thuringia. These states had been the original five states of East Germany before being abolished in 1952 and had been reconstituted in August. East and West Berlin were reunited as a city-state, which became the capital of the enlarged Federal Republic.
After the fall of the Berlin Wall, Kohl affirmed that former German territories east of the Oder-Neisse line were definitively part of Poland, thereby relinquishing any claim Germany had to them in a treaty signed on 14 November 1990 in Warsaw. Though earlier in March of that year, Kohl caused a diplomatic firestorm when he suggested that a reunified Germany would not accept the Oder–Neisse line, and implied that the Federal Republic might wish to restore the frontier of 1937, by force if necessary. After the statement caused a major international backlash that threatened to halt German reunification, Kohl retracted his comments after knuckling under international rebuke and assured both the United States and the Soviet Union that a reunified Germany would accept the Oder–Neisse line as the final border between Poland and Germany. In 1993, Kohl confirmed, via treaty with the Czech Republic, that Germany would no longer bring forward territorial claims as to the pre-1945 ethnic German Sudetenland. This treaty was a disappointment for the German Heimatvertriebene ("displaced persons").
