How secure was the USSR´s control over Eastern Europe, 1948-c. 1989?: Berlin Wall

There was social arrest due to the following reasons:
Quality of life in the West was much better than in the East after 1948. West Hermany had received financial help through the Marshall Plan from USA to rebuild after the devastation of WWII, East Germany had suffered under a communist system after the control of the Soviet Union had been established.
The impact of this mass movement on East Germany was huge.
Socially: Those who left were young and well educated, so red a “brain drain” in East Germany.
Economically: East Germany lost skilled workers.
Politically: Mass numbers were leaving and it made the communist regime look unpopular.