One reason for the construction of the berlin wall in 1961 was to

The soviet union wanted to gain entire control of west Berlin so they cut it off from the rest of the world but this plan did not succeed because the U.S. found a way to bring food and supplies to them by the berlin airlift and the wall remained from 1961 to 1989.
hope this helps.

The Berlin wall was built to keep people in communist Germany. The German authorities thought that too many people were fleeing so they built the wall overnight. 

Well, then we all die