Kept: 3 October
On 3 October 1990 the German Democratic Republic stopped existing and joined the Federal Republic of Germany. For the first time since 1945, there was one German state. The same day, East and West Berlin became one city again.
The wall had come down on 9 November 1989. The two halves became one almost a year later. The falling and the becoming were not the same day.
Kept.