The communist government of East Germany began building the Berlin Wall on August 12, 1961. The Berlin Wall divided Berlin from 1961 to 1989.
The Wall completely cut off West Berlin from surrounding East Germany and from East Berlin. The barrier included guard towers placed along large concrete walls.
Before the Wall's erection, 3.5 million East Germans had defected from East Germany, many by crossing over the border from East Berlin into West Berlin Between 1961 and 1989, the Wall prevented almost all such emigration. During this period, around 5,000 people attempted to escape over the Wall, with an estimated death toll ranging from 136 to more than 200.
The U.S. government responded angrily, but did nothing. President John F. Kennedy believed that “A wall is a hell of a lot better than a war.”
In an attempt to reassure the West Germans that the United States was not abandoning them, Kennedy traveled to the Berlin Wall in June 1963, and famously declared, “Ich bin ein Berliner!” (“I am a Berliner!”).
Berlin Wall became a physical symbol of the Cold War and the stark difference between communist East Berlin and democratic West Berlin.
In a speech in West Berlin on 12 June 1987, U.S. President Ronald Reagan challenged Mikhail Gorbachev, then the General Secretary of the Communist Party of the Soviet Union, to tear down the Wall as a symbol of increasing freedom in the Eastern Bloc:
"We welcome change and openness; for we believe that freedom and security go together, that the advance of human liberty can only strengthen the cause of world peace. There is one sign the Soviets can make that would be unmistakable, that would advance dramatically the cause of freedom and peace. General Secretary Gorbachev, if you seek peace, if you seek prosperity for the Soviet Union and eastern Europe, if you seek liberalization, come here to this gate. Mr. Gorbachev, open this gate. Mr. Gorbachev, tear down this Wall!"
In late 1989, with communist governments falling throughout Eastern Europe, the Berlin Wall was finally opened and then demolished. For many observers, this action was the signal that the Cold War was finally coming to an end.
To learn more about the Berlin Wall go here and here.