The infamous Berlin Wall served to physically divide the city of Berlin into Soviet occupied East and the free West, and effectively cut off Berlin residents from interaction with each other.
Anyone identified as a West Berlin resident was not allowed to travel in the Eastern sector, for other citizens of West Germany entry was possible but travel was severely inhibited.
The collapse of East German control began with an announcement on November 9, 1989 that East German residents would be allowed to cross the border, at which point a mass exodus began. Actual demolition of the wall and official reunification of the city of Berlin did not occur until the following year, but on November 9th the die was cast.
Though this is not an official U.S. holiday I do believe it is a day for us to celebrate.
~ Bill