Wikipedia. The Day of German Unity (German: Tag der Deutschen Einheit) is the national day of Germany, celebrated on 3 October as a public holiday. It commemorates the anniversary of German reunification in 1990, when the goal of a unity of Germany that originated in the middle of the 19th century, was fulfilled. Therefore, the name addresses neither the re-union or union but the unity of Germany.
Before reunification, in West Germany the "Day of german Unity" (Tag der deutschen Einheit, without capital D) was 17 June, remembering the failed Uprising of 1953 in East Germany against the Stalinist government. The revolt was crushed with Soviet aid; the exact number of fatalities is unknown, but estimated at somewhere above 100. In East Germany, the national holiday was 7 October, the "Day of the Republic" (Tag der Republik), commemorating the founding of the German Democratic Republic in 1949.
An alternative choice to commemorate the reunification could have been the day the Berlin Wall came down—November 9, 1989, which coincided with the anniversary of the proclamation of the German Republic in 1918 and the defeat of Hitler's first coup in 1923. However, 9 November was also the anniversary of the first large-scale Nazi-led pogroms against Jews in 1938 (Kristallnacht), so the day was considered inappropriate as a national holiday. Therefore, 3 October 1990, the day of formal reunification, was chosen instead.