The Berlin Wall was opened on the 9th of November, 1989.
That summer, a large number of people left East Germany via Hungary. Later, they went through Czeckoslovakia. Demonstrations and a Peaceful Revolution culminated in the government of East Germany deciding to allow refugees to cross the border freely.
A combination of events--TV broadcasts of the announcement, poor communication between leadership of the German Democratic Republic and the soldiers at the gates, a crowd of people wanting to leave, and no one willing to issue orders to kill protesters at the Wall--led to the guards at the gate letting people through.
The Wall was opened that November. It was not torn down for some time after.
It was the beginning of the end of the Warsaw Pact. And it was the foreshadowing of the fall of Communism in the Soviet Union.