What was the purpose of the Berlin Blockade?

In 1948 and 1949, Stalin decided to impose a blockade on West Berlin as part of an overall plan to bring West Berlin, then the whole of the western portion of Germany (still occupied by French, British, and American forces), into union with Soviet-controlled East Germany. By closing land-access to West Berlin, Stalin considered that the city would soon require Soviet assistance and thereby come under Soviet control.