Who: The Berlin Wall was built by the communist government of East Germany who were known as the Soviet Union. The Soviet Union were going up against the United States, France, and Britain.
What: The Berlin Wall made it so that no one in East Berlin could have access to West Berlin.
Where: The wall was placed right in the middle of Berlin Germany, it separated West Germany which France, The United States, and Britain owned and East Germany which the Soviet Union owned.
When: 1949 through 1960 over two million people left East Berlin to go to West Berlin. In 1961 the Berlin Wall was built. On November 9 1989 the Berlin Wall was taken down and after 40 years in 1990 Germany rejoiced.
Why: The Berlin Wall was built so that no others could leave East Berlin because they could not afford to lose all those people. West Germany and East Germany rejoiced because President Ronald Reagan gave a speech which made up the Soviets Unions minds.
Summary: The Berlin Wall was built to prevent people from leaving their side of the country, it was built in 1961 and the Soviet Union was the one who built it for that reason.