Simplify the following text for a Grade 7 native English-speaking person.
Original: Charlottenburg was an independent city to the west of Berlin until 1920 when it was incorporated into `` GroÃ - Berlin '' ( Greater Berlin ) and transformed into a borough .
Simplified: Charlottenburg was an independent city to the west of Berlin until 1920 . Then it was made part of GroÃ - Berlin ( Greater Berlin ) and turned into a borough .