West Berlin
As the Cold War continued, many East Germans began leaving East Germany for the West. East Germany closed the borders between East and West Germany in 1952, but did not seal off West Berlin; because there was freedom of movement between West Berlin and West Germany, Easterners could use the city as a crossing point to the West. To stop this drain, the East German government built the Berlin Wall, thus physically closing off West Berlin from East Germany, on 13 August 1961. It was still possible to travel from West Berlin to West Germany by air and by specific rail and autobahn transit routes set aside for that purpose, but inhabitants of the two Berlins were now physically and legally separated from each other.