What led to the construction of the berlin wall?

There was a refugee crisis in Berlin, where East Berliners would flee to West Berlin in the prospect of employment, more freedom and a better standard of living. East Berlin was ruled by the communist Soviet Union, and West Berlin by the capitalist USA. The emigration of East Berliners to West Berlin created a propaganda crisis for the Soviet Union as it showed the world that people preferred capitalism over communism. The wall was built to stop people fleeing.